(あなた) 日本に帰っていますか?
(Anata wa) Nihon ni kaette imasu ka?
The "Anata wa" is not necessary if you use the sentence in a context that makes it clear that you are asking about the person hearing the question. It's also possible to use the person's name as in "Kumiko-san Nihon ni kaette imasu ka?" but that's more formal than just simply asking "Nihon ni kaette imasu ka?"