Wh- Questions words: Who…?

Wh- questions always begin with one of the wh- question words (interrogative pronouns), which show what kind of information is wanted {see Wh- Questions, A1 Level}.

The pronoun who is used to ask about the subject of the action.

https://open.books4languages.com/english-a2-grammar/chapter/wh-questions-words-who/