I was hoping someone who speaks Mandarin would answer, but none so far.. So please allow me to answer in English. Sorry. Does your question mean "After いつ, when to use か, and when to use に？" いつか means someday(in future). It's not a question. 「いつか日本へ帰りたいです」 I want to go back to Japan someday. We don't say いつに usually. Just いつ is enough to ask "when?" 「いつ来ましたか？」When did you come?