W____is that man ?

Where is that man ? (问那人的位置)
Who is that man ? (问那人是谁)
What is that man ? (问那人的职业)

Who is that man?

Where is that man? (那人在哪儿？)
Who is that man? (那人是谁？)
What is that man? (那人是干什么的？)
Why is that man? (怎么会是他？特殊用法，比如不想看见此人时)