The usual interrogative pronouns are: who, whom, what, which, when, where, why, how. What and which can also be used as interrogative determiners.
- Who’s coming?
- Who(m) did you help?
- Where do you live?
- When do you want me to come?
- Why did he leave so early?
- How do you want it cooked?
- What did you buy for her?
- Which is your favourite?
Note: What and which, no matter whether they are used as pronouns or determiners, have different implications. What signals that there are many to choose from, which that the number is limited.
- A: What would you like to listen to?
- B: I’d prefer a Beatles CD? A: Which (one)?
- Which of you is John Stockwell?
- Who is John Stockwell?
Whom is rarely used as an interrogative pronoun. It feels very formal. After a preposition, the informal alternative is to put the preposition at the end.
- Who(m) do you want to invite?
- With whom did you share the pizza?/Who did you share the pizza with?
- How is his daughter? (a question about somebody’s temporary health/state of mind)
- What’s his daughter like? (a question about somebody’s nature/permanent qualities)