The grammatical term for "whose cake is the best" is a question. It is an interrogative sentence, specifically asking about the ownership or possession of the best cake among a group of cakes. To determine the grammatical name of a sentence, you typically need to look at its structure and function within the context of a sentence. In this case, "whose" is a possessive pronoun used to indicate ownership, "cake" is the subject, "is" is the linking verb, and "the best" is an adjective phrase modifying the subject.
