Answer:
Subject
Step-by-step explanation:
A subject refers to the person, object, event, place, idea, being, etc. (whether plural or singular) that is being discussed, described or dealt with in a sentence, and a subject may be a group of words (like phrases or clauses) or just one (E.g. "I" and "Mary"). In the sentence, "Whatever you tell me" is acting as a noun and a subject: It is the main focus in the sentence and it's what is being dealt with.