To ask one how their day is going, how they are feeling, or both. Similar to "How's she goin'". As for the nature of the question people tend to respond with "She" or "Blow" since it fits nicely, keeps a dirty twist on an everyday question.

"Blow" used in this context is not in anyway negative, when "she" blows, "she" should be blowing good otherwise you should think of finding a new one.

Literally everyone, ever. Including the writer of this definition.