I didn’t know that how to answer the question._______错在哪?为什么

I didn’t know that how to answer the question._______
错在哪?为什么

I didn’t know how to answer the question
that去掉.
我不知道怎么回答问题.

that去掉.

I didn’t know how to answer the question
that去掉.
我不知道怎么回答这个问题.