Who was the target audience of the Book of Job?

The book of Job is addressed mostly to those who find themselves at the mercy of God, going through inexplicable pain, loss and/or despair, despite living upright life.

“There was a man in the land of Uz whose name was Job, and that man was blameless and upright, one who feared God and turned away from evil.” ‭‭Job‬ ‭1:1‬ ‭

It is written to shed light on the divine council and the judgments that take place at the judgment seat and how the accuser can have legal rights to oppress such a man, as well as recognize that God only allows these circumstances because He sees it as a last resort to getting through to such a man.

“Then Satan answered the Lord and said, "Does Job fear God for no reason? Have you not put a hedge around him and his house and all that he has, on every side? You have blessed the work of his hands, and his possessions have increased in the land. But stretch out your hand and touch all that he has, and he will curse you to your face."” ‭‭Job‬ ‭1:9-11‬ ‭

His arguments are actually very weak and he is granted legal rights with limitations in-spite of and not because of his arguments.

The reason Job was allowed to be tested in this manner was because Job was in a dangerous position. Job had started to attribute God’s righteousness to himself. Job had slapped a sticker with Job’s Name on God’s righteousness. And that is pride.

Notice God instigates the questions, almost leads the accuser on.

“So these three men ceased to answer Job, because he was righteous in his own eyes.” ‭‭Job‬ ‭32:1‬ ‭

God in the Hebrew never calls Job righteous in the whole book. Righteousness belongs to God.

“I will get my knowledge from afar and ascribe righteousness to my Maker.” ‭‭Job‬ ‭36:3‬ ‭

When Job finally realizes that all his success was not because of his upright, blameless, God fearing living but because of God, He repents and he is restored.

This book is especially for those who can fall prey to pride, relying on their own wisdom, righteousness and/or strength. God resists the proud and will even instigate the accuser to put someone straight.

“"Adorn yourself with majesty and dignity; clothe yourself with glory and splendor. Pour out the overflowings of your anger, and look on everyone who is proud and abase him. Look on everyone who is proud and bring him low and tread down the wicked where they stand.” ‭‭Job‬ ‭40:10-12‬ ‭

It’s a tricky place to be. Live upright and with fear of God but attribute God’s righteousness to yourself over time. It’s so subtle and the nicest thing God can do is draw your attention whatever it takes, in order to save your soul.

As Nigel J suggested in his comment, the book of Job is addressed to every single person on earth. Its “target audience” is every human who has ever lifted his eyes to heaven and cried out, “Why me, God?” It’s God’s message to all of humanity to remind them that He is sovereign, that His judgments are righteous and it isn’t the place of mere mortals to question or challenge Him.

Two of the unanswerable questions presented by the book of Job are (1) When did Job live? (2) Who wrote the book, and when was it written? Here is some useful information I found regarding this:

NLT Study Bible Notes: The authorship and composition of Job is a riddle. Although the story has a patriarchal setting (around 2000 B.C.), the date of its composition appears to be much later. Commentators have suggested dates that range from the era of Israel’s wilderness wanderings to the era following the return from exile. The final composition of Job probably took place during the monarchy when other wisdom materials such as Proverbs and Ecclesiastes were being accumulated. The earliest reference to Job is during the Exile, in Ezekiel 14:14, 20.

NIV Study Bible Notes: The author was an Israelite, since he frequently uses the Israelite covenant name for God (Yahweh)... While the author preserves much of the archaic and non-Israelite flavour in the language of Job and his friends, he also reveals his own style as a writer of wisdom literature.

The Book of Job does not specifically name its author. The most likely candidates are Job, Elihu, Moses and Solomon. The date of the authorship of the Book of Job would be determined by the author of the Book of Job. If Moses was the author, the date would be around 1440 B.C. If Solomon was the author, the date would be around 950 B.C. Because we don’t know the author, we can’t know the date of writing. https://www.gotquestions.org/Book-of-Job.html

Understanding the background to this masterful piece of Wisdom Literature helps us to grasp the fact that Old Testament events affecting God’s chosen people were divinely preserved and recorded to educate all who are created in the image of God. It wasn’t just written for the Israelites although it undoubtedly resonated strongly with them. The book of Job has a universal message:

God challenges Job’s right to question the integrity of divine justice (Job 40:8)... God’s holy purposes for human suffering are sometimes hidden. Yet in the end, Job draws closer to God through his suffering: “I had only heard about you before, but now I have seen you with my own eyes” (Job 42:5). Source: NLT Introduction to the book of Job

The events that took place circa 2000 B.C. were as relevant and meaningful then as they are today.

Now the question of who is the target audience for Job is a tricky one, because there is the audience that Job intended, and the audience that God intended. Since the book is not addressed to a group as are Paul's letters, or to a son as is the Book of Proverbs, or to Theophilus as are Luke and Acts, the best clues come from understanding the purpose of the book.

In Job 19, the suffering man says this:

23 “Oh that my words were written!
    Oh that they were inscribed in a book!
24 Oh that with an iron pen and lead
    they were engraved in the rock forever!
25 For I know that my Redeemer lives,
    and at the last he will stand upon the earth.
26 And after my skin has been thus destroyed,
    yet in my flesh I shall see God,
27 whom I shall see for myself,
    and my eyes shall behold, and not another.
    My heart faints within me!

Job wanted the world to know that he believed that God would raise him from the dead.

God wanted the world to know that Job spoke the truth about Him:

7 After the Lord had spoken these words to Job, the Lord said to Eliphaz the Temanite: “My anger burns against you and against your two friends, for you have not spoken of me what is right, as my servant Job has. (Job 42:7)

And what was this truth that Job spoke? If you read Job's speeches carefully, you will see that out of his suffering he speaks prophetically about the coming savior and about many other events that were to come to pass. Evidence in the book points to it being written between the times of Abraham and Moses. The book is filled with examples of the several approved ways that God communicates with mankind, including sacrifice, looking for clues in nature, listening to wise elders, prayer, fasting, sabbath observance, dreams, visions, suffering, angels, and theophany. Job's prayer in chapter 19 cited above is a new contribution: the Word of God in written form. Just as Abraham prayed for a son and was blessed to become the father of many nations, so Job's prayer was answered beyond his wildest expectation: his story would become the first book of the Bible to be written down.

Job's main prophecy was that God was about to construct a written record of his dealings with mankind so that all people could know clearly what God expected of them and how to seek his favor. Thus Job's audience in general was the whole world. But in particular, you will see that many verses in Proverbs have their echo in Job, as do the Psalms, Ecclesiastes, Jeremiah, Revelation and even the words of Jesus in the Gospels. So another important audience was the prophets.

Amos said this in 3:7:

“For the Lord God does nothing
    without revealing his secret
    to his servants the prophets."

If Job is the first book in the Bible, then it stands to reason that, in addition to words about what would happen in the distant future, Job would leave instructions to guide people by telling them what would happen in the near future, to authenticate his next prophet. And so he does. The Bible has many references to papyrus as a symbol of the fragility of life.

Can **papyrus** grow tall where there is no marsh? 
Can reeds thrive without water? (Job 8:11)

Which will be reversed when the savior comes:

The burning sand will become a pool,
    the thirsty ground bubbling springs.
In the haunts where jackals once lay,
    grass and reeds and **papyrus** will grow. (Isaiah 35:7)

Papyrus when formed into a swift boat is used to describe people trying to outrun God's judgment:

Woe to the land of whirring wings
    along the rivers of Cush,
2 which sends envoys by sea
    in **papyrus** boats over the water. (Isaiah 18:2)

In a chapter where Job says he cannot see God, he speaks of God walking on the seas:

He alone stretches out the heavens
    and treads on the waves of the sea. (Job 9:8)

This is ironic, since a man who says he cannot see God has just given a prophecy of Jesus walking on water! (Saint John Chrysostom noted this centuries ago.) In that same chapter, Job says this:

“My days are swifter than a runner;
    they fly away without a glimpse of joy.
26 They skim past like boats of **papyrus**,
    like eagles swooping down on their prey. (Job 9:26)

Job speaks of a swift papyrus boat as reflecting how fast his life is moving towards death. The context is the midst of a storm:

He would crush me with a storm
    and multiply my wounds for no reason. (Job 9:17)

Would you want to weather a storm in a boat made of papyrus? Not safe! So Job gives the image of a swift boat made of a material not fit for stormy weather, a material that cannot save him from a swift death. So can a papyrus boat save someone marked for death? Can the Lord make Job's words ironic and deliver a soul from a watery grave?

3 But when she could hide him no longer, she got a papyrus basket for him and coated it with tar and pitch. Then she placed the child in it and put it among the reeds along the bank of the Nile. Exodus 2:3

Who was placed in a papyrus basket and saved from drowning in the Nile? Moses!

So I would say that the immediate audience for Job was the Hebrew people, to endorse their great prophet, Moses, a man who would pen a large part of the Old Testament, and likely do so on scrolls made of papyrus.