I was wondering if there is a difference if you add that ん. Is the first one correct and the second one not?
男じゃないんですか?
男じゃないですか?
I think the difference is how long you assumed that the person is a man. 「男じゃないんですか?」 implies that you've been assuming that the person is a man for some time. On the other hand, 「男じゃないですか?」 implies that you have just realized that the person is a man (though, it depends on the emphasis. You would put the emphasis on the word 「ない」 in this case).
sentence+の/ん+copula+か
. If thesentence
ends on the copula だ, it becomes な, giving なのか or なのですか/なんですか. If it ends on the negated copula じゃない, you get じゃないのか or じゃないのですか/じゃないんですか. As I understood it, the question was about the presence of ん/の, not the negated phrase before it.