Watch the following picture:
This is a SUBJECT QUESTION. This type of questions ask about the subject of the sentence.
There is no auxiliary verb.
The order of the question is not changed.
What has John got? John has got a puppy.
This is an OBJECT QUESTION. This type of questions ask about the object of the sentence.
We need the auxiliary verb.
The order of the question must be changed.
Who told you?. Mary did it.
Who lives here? Mary does it.
What killed the dog? A car did it.
Who did you tell?. I told Mary.
What does she usually read? She usually reads poetry.
Who does she know? She knows these two guys.