I don't know how I do it, "he said."

“我不知道我是怎么完成这一切的，”他说。

youdao

I don't know how he could do this to his own daughter.

我真想像不出他怎么能这样对待自己的女儿。

《柯林斯英汉双解大词典》

I don't know what the teacher is saying and I don't know how to do homework, either.

我不知道老师在说什么，我也不知道如何做家庭作业。

youdao

I don't know how many kids, generation after generation, get in trouble because they do not remember the following fact.

我不知道有多少孩子,一代又一代,因为没有记住下面的内容而遇到困难

耶鲁公开课 - 基础物理课程节选

And secondly, I think that, even if they don't know how to do a problem,

二是，我觉得，即使他们不知道怎么做一道题，

体罚是不可取的 - 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

"I don't know how they do that, on what basis they make their judgment, I don't suggest it's a top 20, who is that person who is going to be more favourable to the Met than others, but I was told that system existed and I quite believe it, " he said.

BBC: Leveson Inquiry: Lawrence leak had 'negative effect'

"I don't know how operas are supposed to be, but I do know when I'm bored, " Mr. Shanley says.

WSJ: A Re-'Doubt'-able Effort | John Patrick Shanley | Cultural Conversation by Judith H. Dobrzynski

Mr. THOMPSON: I don't know how long Mr. Rumsfeld intends to stay but I do know this - he's not going to leave under fire.

NPR: Donald Rumsfeld, Secretary of Self-Defense