2. Used after a noun or pronoun to show which group of people someone is talking about: "Children who are interested in joining the play group should come tomorrow."
3. Used to introduce an additional statement about someone who has already been mentioned: "Brandon, the neighbor who lives next door, takes care of the house that belongs to Pamela and her family when they are on vacation."
"Heather, Roy's sister, with whom he is very close, works for another business."
Whom is a more formal word than who and is not commonly used in ordinary speech and writing, where it can seem awkward and unnatural."
Who do you think is pretending to be an owl and whispering WOOO, WOOO, WOOO in the garden? To whom are you directing your question?