How to express “What are you doing ?” and how to answer it in Chinese? it’s very simple.
Q: What are you doing ? 你在干什么？ 你在做什么？
A: I am + v 我在+（动词）such as playing football
sample:
Q: 你在干什么？What are you doing ?
A: 我在看电视。I am watching TV.
Q: 你在做什么？What are you doing ?
A: 我在写日记。I am writing diary.