Whose? – чей

1. Глагол to be.

We are doctors in a hospital. → Where are you doctors?

He was there 2 hours ago. → When was he there?

2. Смысловой глагол.

I like coffee. → What do you like?

Helen watches TV every day. → How often does Helen watch TV?

3. Модальный глагол.

I can swim well. → How can you swim?

He must do it immediately. → When must he do it?