Final answer:
Snape assigned essays on the use of moonstones and werewolves to Harry's class at Hogwarts.
Step-by-step explanation:
During his time at Hogwarts, Professor Snape set Harry's class several essay assignments. Among these subjects, Harry was tasked with writing about the use of moonstones for potions and werewolves.
The essay on moonstones was assigned to prepare Harry and his classmates for their O.W.L. (Ordinary Wizarding Level) exams. Additionally, Snape assigned an essay on werewolves which was seen as a thinly veiled reference to Professor Lupin's condition.