他不知道吧？——不，他知道。

He doesn't know, does he? — Yes, he does.

《新英汉大辞典》

你不会不知道吧？

I doubt you don't know.

《新英汉大辞典》

你大概不知道吧，他膝盖做手术了。

B: I guess you didn't know that he had an operation on his knee.

youdao

Right? That would be an entirely different matter, wouldn't it, because you would have absolutely no idea whether the question was rhetorical or grammatical, right?

对吧，那将会是一个完全不同的情况，难道不是吗，因为你就会完全不知道,这个问句是修辞型的还是语法型的，对吧？

耶鲁公开课 - 文学理论导论课程节选

You have to have at least, I don't know, cereal or maybe a piece of fruit?

你至少得吃点，我不知道，也许吃点麦片或者吃块水果吧。

Have you 实战 - SpeakingMax英语口语达人

But if you say, well, I don't know how to do this, I am not going to bother, don't grade the paper.

但是如果你说，好吧，我不知道怎么做这个，我想麻烦，别给试卷评分。

麻省理工公开课 - 固态化学导论课程节选