He wrote the music but I don't know who wrote the words.

他创作了乐曲，但我不知道谁填写的歌词。

《牛津词典》

But I don't know who he is.

但我不知道他是谁。

youdao

Someone has used my bike, but I don't know who (has used it).

有人用了我的自行车，但我不知道是谁。

youdao

"I know a lot of schools have their own newspaper or newsletter, but don't know of many who have a newspaper for the school that's part of a reservation-wide or huge area-wide publications."

VOA: special.2011.04.07

I don't know how many of you have not read any Plato before, but for those of you who haven't, I actually think you're in for a treat.

我不知道你们当中有多少人,之前未曾读过柏拉图的作品,但是,还未拜读过柏拉图的同学们,我敢肯定你们会喜欢上他的

耶鲁公开课 - 死亡课程节选

This guy--I don't know who he is but he seems to be on a lot of these things but the thing is you don't need to rely on him.

这个家伙，我不知道他是谁,不过他看起来在很多这类地方出现,但你不必依赖他做的表情。

耶鲁公开课 - 心理学导论课程节选

Someone -- and I wish I could tell you who, but I don't know who -- someone brought to that group a proposal that we authorize a request from the Saudi embassy.

CENTERFORSECURITYPOLICY: Center For Security Policy

"I'm not ready to have him come back and run the police department, but I don't know if I'm ready for this either, " said Triplett, who sided with the majority to reject the resignation.

CNN: STORY HIGHLIGHTS

But I don't know - again, I think what works about this is that they're the ones who really know what's different about the two of them.

NPR: Coldplay, Katy Perry and More New Releases