I went very literal but "Do you have certainty" should be valid
"Are you certain" is also a valid translation of this sentence.
Should "You are certain?" also be acceptable if "Are you certain?" is?
Yes, in fact this is how they ask questions in Portugal all the time. Are you certain? should be accepted.
Technically you are certain is not a question. There is no question word to indicat a question. It is a statement
If you follow it with a question mark and raise the intonation at the end of the sentence it is a question.