What answers what and whom?

In English grammar, "what" is used to ask about things or ideas, while "whom" is used to ask about people or objects that are the object of a verb or preposition. "What" is used for subjects and direct objects, while "whom" is used for indirect objects and objects of prepositions. For example, "What are you reading?" asks about the thing being read, while "Whom did you give the book to?" asks about the person receiving the book.