I don't know what to do with it. （这种情况下）我不知道该怎么办？with it 表示在这种情况下。
这句话和 I don't know what to do.(我不知道该做什么)还是有细微的区别的；
以及和 I don't know how to do it.(我不知道该怎么做这件事）也是有区别的，仔细体会下哦。
使用语境：
Tom: Why are you so late,David?
你怎么这么迟，David？
David: I met a foreigner on my way to the office. She said that she had a very serious stomachache. As a foreigner, she couldn't speak Chinese and didn't know what to do with it. So I helped send her to the nearest hospital. I am sorry for being too late.
来公司的路上我遇到了一个外国人，她说她胃很疼。她是一个外国人，不会说汉语，不知道该怎么办，所以我就帮忙送她到了最近的医院。真对不起，我来的太晚了。
相信积累的力量。
英语答疑，每日在线，欢迎关注。