Which在表语从句中充当主语,宾语,表语,定语中的哪些成分?

what he wants to know is which is the best book.which作主语what he wants to know is which you like best which作宾语what he wants to know is which the best book is .which作表语what he wants to know is which book is the book which作定语 this is what makes you happy.what 作主语this is what he wants.what 作宾语the question is what he is .what 作表语the question is what language he wants to learn.what 作定语

which 可以充当定语 主语 宾语 但不可以充当表语