不知道是谁的英文

“不知道是谁的”翻译成英文是：I don't know who it is.

I don't know who/whom she is.口语中可用whom,正式的书面语用who.宾语从句中是陈述句语序即:主语+动词+其它。

可以直接翻译为：I don't know who it is。