Upvote:4
In principle, you can be asked pretty much everything, to establish that you have a valid purpose of stay and fulfil all the other conditions (financial means, intent to leave the area, etc.). So hotel booking, itinerary, etc. and, as Michael explained, everything you would need for a fresh visa application might come in handy.
But that's not specific to the second trip, it was also the case for your first trip. In practice, the fact that you are entering France on a German visa could prompt border guards to inquire a bit more than usual but on the other hand having a multiple-entry visa that you have already used is a plus so I would not generally expect many questions.
You also need to have a valid travel health insurance (you only had to prove you had insurance for the first trip when applying for the visa but you are required to be covered for each subsequent trip as well). I have never heard anyone tell me they actually had to prove that, but that's a requirement nonetheless.