你在说什么我一点都不懂。

I don't have the remotest idea what you're talking about.

《牛津词典》

当我听不懂老师在说什么时，我就会走神。

I will lose concentration when I can't understand what the teacher is saying.

youdao

我弄不懂他在说些什么。

I couldn't make head nor tail of what he was saying.

《牛津词典》

Yes, I see them in the text just as anybody else does, but since I don't really know what they mean except by means of the translation, why should I use them?

我看着这些原版书，但是我也不懂他们真正什么意思,除了它们翻译过来的意思，所以我干嘛费劲去用俄语？

耶鲁公开课 - 文学理论导论课程节选

But the students, they think that I'm an old woman from the cave and I don't know anything

但学生们认为我是住在洞穴的老女人，我什么也不懂，

对于抄袭的想法 - SpeakingMax英语口语达人

If you haven't turned it on or don't know what that thing is here we go.

如果还没用过它,或者不懂它是什么,请看下面。

哈佛公开课 - 计算机科学课程节选