We use interrogative pronouns to ask questions. The interrogative pronoun represents the thing that we don't know (what we are asking the question about). There are four main interrogative pronouns: who, whom, what, which .

Besides this, possessive pronoun whose can also be an interrogative pronoun (an interrogative possessive pronoun).

Example :
1. Who told you?
2. Whom did you tell?
3. What do you want?
4. Which came first?
5. There's one car missing. Whose hasn't arrived?