Solution:
- He's the teacher who helped me to pass the exam.
- That's the school where I went when I was five.
- Do you remember the time when I fell into the river?
- She's the girl whose father is an actor.
- Have you read the essay that I wrote?
- This is the email which came yesterday.
Answer: 1. who, 2. where, 3. when, 4. whose, 5. that, 6. which.