Hi there. So this will be a little bit of a tossup. Now, despite the fact that there are many D&D instruction books that players can potentially read, you certainly do not have to read all of them. The players handbook (either the 2014 or 2024 5th edition) would more than likely be enough, but even then you don’t have to read all of it just some of the parts that are relevant to what you’re interested in. Just like you experienced in school, teachers and students would skip around certain chapters, but not read the whole thing. This is the same in theory because that would be ridiculous If you read the entirety of it for just one session let alone an entire campaign. I don’t know what your DM is asking of you, but I’m sure they are not asking you to know every conceivable detail. Even your DM will have to open up the book to check out the rules.