It's a question without answer. / It's a question with no answer. It's a question which has no answer. / It's a question which hasn't answer. / It's a question which doesn't have answer. It's a question without AN answer / It's a question with no answer. It's a question which has no answer / THIS ONE IS INCORRECT / It's a question which doesn't have AN answer. These all mean the same thing. :)

They are correct in grammar, but "It's a question with no answer" seems more natural.