"You know how to dance" is a statement not a question . "Do you know how to dance" ? is the correct question form . But in everyday use or daily communication with people they might ask you in the first form "you know how to dance?" and of course their tone will indicate if it is a statement or a question !

Oh, just kidding, i thought you were asking for it in english :X

"You know how to dance." lol... you already did it :] to make it a question, you have to end it with a "?"