她不明白那笑话的含义。

She didn't get the joke.

《牛津词典》

她不明白所涉及的事情。

She had no comprehension of what was involved.

《牛津词典》

她不明白怎么会有人竟拿人们的生命那样去冒险。

She could not comprehend how someone would risk people's lives in that way.

《牛津词典》

She didn't know why but she listened to him after all-- he was Gandhi.

她不明白为什么但还是听了他的话-,因为他是甘地。

哈佛公开课 - 幸福课课程节选

But you can't put your finger on what the source of that confrontation was.

但是你还是搞不明白为什么她老是要跟你对着干。

I don't know 课堂 - SpeakingMax英语口语达人

I don't know why she dislikes me.

我真不明白她为什么不喜欢我。

I don't know 课堂 - SpeakingMax英语口语达人