Professor Weasley will give you an assignment where she will ask you to obtain a field guide page from the Intermediate Transfiguration book in the library. The library in Hogwarts castle is quite large so finding the book is a bit tricky. Your character will give you some prompts but nothing concrete. Here is where to find the book.
You will need to head up to the upper level of the library and go to the side opposite of where the stairs bring you up. In the back corner, you will find a girl who is reading and standing around. If you spend enough time around her, she will show up with a quest marker and you will be able to speak with her.
When you speak with her, she will give you a quiz. I got a few wrong answers but she still gave me the book. The answers should be Golden Sniddich before the snitch. Quaffle is the biggest ball. Deathly Hallows are the three items.
Once you finish the quiz, she will put the book back on the pedestal and you can then cast revelio to view the field guide page.