Expecting an answer like these,
1. I'm happiest when I'm with you.
2. I'm happiest when I play tennis.
3. I'm happiest when I'm sound asleep.
which is an appropriate question?
1. In doing what, are you happiest?
2 What are you doing when you are happiest?
3 When are you happiest?
4. Any other?
+ What gives you the most happiness?