How are you与How are you doing，有何不同呢？

貌似没有不同……

中国教科书式的回答是"Fine, thank you, and you?"

随便一点"Great/Wonderful/Well/Good/Not bad"

有区别的是How do you do?

这个的回答一般比较固定就是同样来一句How do you do?

ref:

http://english.stackexchange.com/questions/73766/difference-between-how-are-you-and-how-are-you-doing

How are you vs How are you doing