Answer

An interrogative sentence is a sentence whose grammatical form shows that it is a question. Such sentences may exhibit an interrogative grammatical mood.

So according to this, the interrogative form of " You  can dance" would be:

"Can't you dance ? "

An interrogative sentence asks a question. This type of sentence often begins with who, what, where, when, why, how, or do, and it ends with a question mark. Also, if the sentence is in positive tone, the interrogative sentence of this would turn in a negative tone with the same verb used in the affirmative sentence.