翻译：你知道他什吗时候回来吗？

Do you know when he will come back?

楼上错了，后面应该用陈述语气。

Do you know when will he return?
Do you know what time will he return?

Do you know when he will return?
Do you know what time he will return?
do you know 作为疑问语气，后面的句子要用陈述语气。

Do you know when he will return

Do you know when he will back

You know? Even when he came back?