How do I practice not-self or Anatta whilst talking?

Let's first look at the self as we usually do. We tend to think that we exist independently from others and everything else. We also tend to feel the self is fixed, permanent. Our body is made up of all sorts of particles (atoms, protons, neutrons, electrons, quarks, etc.) so when we want to locate the self as a body we think it is just a collection of these particles. When we investigate further, we realize that our body, and thereby the self, also interacts with the air around us, the food we eat, radiation from the sun and other sources, the gravitational pull of the earth, moon and sun, other people, etc. Basically, we really do not exist as an independent entity apart from everything else. We exist interconnected to everything else in the universe. There really is no self that exists inherently and independently from everything else. This is the concept of non-self (anatta).

Anatta is a concept that falls under the general umbrella of what is called Śūnyatā (emptiness). It is called "emptiness" not because you or other things aren't real or don't exist but because you and everything else is empty of inherent, independent existence. This is called ultimate wisdom which is basically to say that everything is interconnected. Now it is just fine to think that you exist apart from others. This is natural and a way to practically get along in this world. This is part of what is called conventional wisdom. In Buddhism it is valid to view the world with conventional wisdom or with ultimate wisdom. This is part of the "middle path" that the Buddha ultimately advocated.

When you say anatta is when you "think that it's not actually 'my' body" and that "to observe them as if you're an outsider" you are misunderstanding the concept. Conventionally, your body is always your body. You are always you. But on a deeper level your self and your body, feelings, thoughts ,etc. are connected to everything else in the world. This is anatta. When you say you want to "to observe ... as if you're an outsider" this is closer to the vajrayana practice of exchanging self with others.

With this background I can now answer your question. It is totally possible while talking to people to have the mind of anatta at the same time. If while you talk with others you are also continually aware of your interconnectedness with them and everything else then you are practicing anatta and ultimate wisdom. If you add selfless love and compassion to this you are basically a bodhisattva and on your way to becoming a Buddha. Everyone has the potential to achieve this because, at our core, we all want peace and happiness and we are all good even though we may go astray. No one is beyond hope. The wish to become liberated for the sake of others is called bodhichitta (the enlightening mind) and is a very powerful way to free yourself from all suffering.

Not-self is an insight. One example is MN 148. You practice on your own and cultivate the insight. Going around saying "the ear hurts" instead of "my hear hurts" is faking it. It won't do much for you.

Impermanence is a gateway into seeing not-self. SN 22.45

What’s impermanent is suffering. What’s suffering is not-self. And what’s not-self should be truly seen with right understanding like this: ‘This is not mine, I am not this, this is not my self.’ Seeing truly with right understanding like this, the mind becomes dispassionate and freed from defilements by not grasping.

ChrisW already touched on this in his answer but it is buried in a bunch of other thoughts, so I'll say it here again:

It's not as much which words you use, as it is what meanings you convey with the words.

The ego is a samskara that reproduces itself by maintaining its stories and narratives. Via these narratives it strives to prove its own significance and "rightness" - to itself and to the world. Oftentimes we ourselves do not notice how the ego uses our communications to defend, rationalize, and self-promote.

The best you can do to practice anatta "whilst talking" is by not allowing the ego to sneak its agenda into your messages. This requires cultivating a high degree of self-awareness and critically scrutinizing every single word you say to see if any of it serves a hidden purpose to self-aggrandize, rationalize complacency, or otherwise feed the ego.

There's not much else to it, but you must realize that ego is an extremely tricky and clever mechanism and it will try to do its thing in very sneaky ways, despite your best efforts.

Starving the ego is a quintessential Mahayana practice and its importance cannot be overemphasized. For more information on this practice, I recommend studying Chogyam Trungpa's 'Cutting through spiritual materialism'.

While SN 1.25 presents this from the arahant's perspective, SN 22.89 presents this from the stream enterer's perspective.

The Venerable Khemaka replied:
“These five aggregates subject to clinging have been spoken of by the Blessed One; that is, the form aggregate subject to clinging … the consciousness aggregate subject to clinging. I do not regard anything among these five aggregates subject to clinging as self or as belonging to self, yet I am not an arahant, one whose taints are destroyed. Friends, the notion ‘I am’ has not yet vanished in me in relation to these five aggregates subject to clinging, but I do not regard anything among them as ‘This I am.’” ......

“Friends, I do not speak of form as ‘I am,’ nor do I speak of ‘I am’ apart from form. I do not speak of feeling as ‘I am’ … nor of perception as ‘I am’ … nor of volitional formations as ‘I am’ … nor of consciousness as ‘I am,’ nor do I speak of ‘I am’ apart from consciousness. Friends, although the notion ‘I am’ has not yet vanished in me in relation to these five aggregates subject to clinging, still I do not regard anything among them as ‘This I am.’
SN 22.89

For a stream enterer, the conceit and habit of "I am" is a deeply ingrained scent or stain that is difficult to be removed and yet to be removed. But being a stream enterer, he does not assume "I am" to be any of the five aggregates.

This is like a person who is still morbidly obese (due to his previous unhealthy lifestyle) but now he fully understands the benefit of healthy living with good diet, exercise, sleep, hydration etc. So, he has already let go of his bad lifestyle habits and bad beliefs, but he still has some distance to go, with a lot of very hard work, before he manages to improve his health and weight.

When he speaks, he uses "I am" without the belief that it refers to his form, feelings, perception, consciousness or volitional formations. But he still has the habit of "I am".

It's a matter of the aggregates, and not you. One thing you could try out is notice how there appears to be a difference in the perception of other people's speaking vs your speaking. What is that particular thing that says: this is mine (you speaking) and that is theirs (their speaking)? Is there really an imaginary partition wall that creates that separation?

There is something in the aggregates that seems to strain reality into two parts: mine and not mine. So, what is that? Is it really a 'that' even?

Because you're looking at the aggregates, one can not find that thing that appears to be the operator, that self, the 'I' that strains reality into two parts. That duality is illusory, in the same way that when you see a rainbow in the sky, you move to investigate it. As your discernment grows closer, the rainbow disappears. From a certain perspective, there appeared to be a rainbow, but upon closer scrutiny, there wasn't.

When speaking happens here, at its bare rudiments, it's noise coming from a hole somewhere. That might sound rather dry, but it can present itself in some very dynamic ways. Apparently, I'm told that great wisdom can exit this hole, but nobody is there to apprehend any of it. That is why the Heart Sutra says: there isn't even any wisdom to attain. However, there are people who can seemingly cognize those noises, which I'm always fascinated by, especially when they have insights or shifts in their awareness.

Similar to SN 1.25 cited in Dhamma Dhatu's answer, there's a Milindapañha which begins,

King Milinda went up to Nàgasena, exchanged polite and friendly greetings, and took his seat respectfully to one side. Then Milinda began by asking:

“How is your reverence known, and what sir, is your name?”

“O king, I am known as Nàgasena but that is only a designation in common use, for no permanent individual can be found.”

Then Milinda called upon the Bactrian Greeks and the monks to bear witness: “This Nàgasena says that no permanent individual is implied in his name. Is it possible to approve of that?”

The "common use" there is similar to the "conventional" in SN 1.25:

Skillful, understanding the world’s conventions,
Loke samaññaṁ kusalo viditvā;

... with "world’s conventions", loke samaññaṁ there, as literally something like "worldly name".

Conventionally, English language grammar has "sentences" which are built using "verbs" and "subjects", and "objects" and so on. There are different ways to use it (i.e. to be expressive or to produce the language) -- for example:

• There's an imperative mood, giving orders: "Cut the grass! Build the house!"
• Or there's a passive voice: "The grass needs to be cut soon."
• FYI I tend to often use an I-message -- because I find that less bossy and argumentative, to say, "I think it's X", instead of, "It is X (and anybody who thinks otherwise is wrong)!"

Pali might not always use explicit words to denote the "subject" in a sentence but I think it might as well, because in Pali the verbs are "conjugated" -- like in Latin for example, the verb amare is "conjugated" as amo, amas, amat, to mean "I love", "you love", or "he or she loves", as different single words -- I don't know if you know a language like that. But I think when you read Pali the "subject" of the sentence may be explicit as a separate word or just implicit (but still implicit), in the conjugation of the verb (which is necessary i.e. conventionally required by the grammar).

In any case I think that, using these languages, it's difficult (or stilted, unconventional) to use the languages "conventionally" without implying that there's a subject and "who" (which person) the subject is.

I think that's maybe less so in some other languages like Chinese -- I don't this know for sure, mind you, I know very little about Chinese -- I think in Chinese you can use an ideogram like "Run" or "Running" without a subject. So you could have a two-word phrase like "run" and "mountain" to say "mountain-running" or "running in the mountain" without implying any particular person who is doing that.

I think there's a form of Buddhist "mindfulness meditation" in English where you're told to think "hearing" when you're hearing something, or "walking" when you're walking. That's maybe similar to the Chinese, i.e. an activity without a subject. It's not conventional dialog though. If we were face to face I could say to you single-words like "grass!" or "hearing!" but that would be kind of odd.

I've definitely seen people (mostly in writing, rarely orally in person) avoid using "first person" (i.e. "I") expression -- for example instead of, "I want X", say, "This person wants X", or even, "She wants X". I think it's good to be sympathetic and permissive to the way people express themselves, but that kind of sentence isn't convention (and other people might find it unusual or uncomfortable). Still it may be what you were asking.

Maybe what's more important or more fundamental isn't grammar but "conceit". I mean this answer:

• How are 'conceit' and 'identity-view' not the same?

Also, more about "conceit" on Wikipedia:

Māna (Sanskrit, Pali; Tibetan: nga rgyal) is a Buddhist term that may be translated as "pride", "arrogance", or "conceit". It is defined as an inflated mind that makes whatever is suitable, such as wealth or learning, to be the foundation of pride. It creates the basis for disrespecting others and for the occurrence of suffering.

I think it may be "conceit" that's in evidence, in the quarrel or harsh words ("wounding each other with weapons of the mouth) depicted in the famous parable of the blind men and the elephant in Ud 6.4.

So I think that may be another answer to your question -- i.e. what's more important than whether you use the word "I" conventionally is whether you think automatically, "I'm right and they're wrong" and so on -- even if that's rephrased impersonally like, "such is truth, such is not" etc.

I said,

In any case I think that, using these languages, it's difficult (or stilted, unconventional) to use the languages "conventionally" without implying that there's a subject and "who" (which person) the subject is.

... but that's not true, or not the whole truth -- because you can write "objectively" in English. I think "objective" is when the grammatical subject of the sentence is some kind of object, something other than a person, and other than personal (e.g. "my feelings" are "personal").

Here's an example of objective writing -- the subject here is the Ear (or "an ear"):

An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. etc., etc., etc.

This implies that you could try to talk about objective or impersonal topics. Here's a page titled Right Speech which quotes nearly a dozen suttas on that topic -- including ones about wholesome and unwholesome subjects of conversation.

I also like this, non-Buddhist discourse -- Bryn Mawr Commencement Address (1986) -- the speaker is an expert skilful with language. It starts with a play on words, then begins to describe "objective" language:

It began to develop when printing made written language common rather than rare, five hundred years ago or so, and with electronic processing and copying it continues to develop and proliferate so powerfully, so dominatingly, that many believe this dialect - the expository and particularly the scientific discourse - is the highest form of language, the true language, of which all other uses of words are primitive vestiges.

And it is indeed an excellent dialect. Newton's Principia was written in it in Latin, and Descartes wrote Latin and French in it, establishing some of its basic vocabulary, and Kant wrote German in it, and Marx, Darwin, Freud, Boas, Foucault - all the great scientists and social thinkers wrote it. It is the language of thought that seeks objectivity.

I do not say it is the language of rational thought. Reason is a faculty far larger than mere objective thought. When either the political or the scientific discourse announces itself as the voice of reason, it is playing God, and should be spanked and stood in the corner. The essential gesture of the father tongue is not reasoning but distancing-making a gap, a space, between the subject or self and the object or other. Enormous energy is generated by that rending, that forcing of a gap between Man and World.

I'll leave you to read the rest if you like. I don't think "objective" language is necessarily better. It has a place or use, it's the language of science, engineering ("The requirement is X, the design is Y"), and probably medicine -- and of a lot of Dhamma. But it's also the language of lies, misunderstandings, half-truths, disputes, bad jokes, and so on, hence my earlier warning against "conceit". It may claim to be "objective" but in fact I think the person is expressing their "view" and to that extent perhaps it's subjective too -- it may be wiser sometimes to phrase as statement as an explicit "I message".

And sometimes I'm not sure it matters -- if a doctor asks "What's the problem?", then whether you answer "There's some pain in the ear" or "My ear hurts", maybe both mean the same thing.

Develop awareness through practising vipassana, and overtime you will be able to observe without thinking, and this is the birth of not-self. Everything else is accomplished through continual practice and time.

At first I practised vipassana for about 3 hours a day, experiencing not self came spontaneously and lasted about 30 seconds; since that time, I meditate and I try to turn activities into meditation. Recommend the miracle of mindfulness, that helped me at the start.

A relevant sutta is SN 1.25.

“When a mendicant is perfected, proficient, with defilements ended, bearing the final body: would they say, ‘I speak’, or even ‘they speak to me’?”

“When a mendicant is perfected, proficient, with defilements ended, bearing the final body: they would say, ‘I speak’, and also ‘they speak to me’. Skillful, understanding the world’s conventions, they’d use these terms as no more than expressions.”

“When a mendicant is perfected, proficient, with defilements ended, bearing the final body: is such a mendicant drawing close to conceit if they’d say, ‘I speak’, or even ‘they speak to me’?”

“Someone who has given up conceit has no ties, the ties of conceit are all dissipated. Though that clever person has transcended identity, they’d still say, ‘I speak’,

and also ‘they speak to me’. Skillful, understanding the world’s conventions, they’d use these terms as no more than expressions.”