确切地讲,How does he do 是不完整的,必须得是类似这样的句子才行：
How does he often do it?他经常怎么做这件事?
How did you do it?你是怎么做的?
How will you do it? 你要怎么做?
用What does he do?就不一样了.类似的句型可以表达很多意思,如：
What does he do? 他是干什么的?是做什么工作的?
What did he do just now? 他刚才做什么了?
What did you do yesterday? 你昨天做什么了?
How ： 怎样,如何.
What： 什么.