Around 40,000 experience points for killing dragons or completing a quest? I always killed them. So, I don't know how much experience they give for a quest. And I don't remember how much I got for the kill.

My personal record is 2.5 million experience points in a single battle. I set it the day before yesterday, fighting 17,000 ents. I guess it could be surpassed by a lot if you take down Nicholas, who has a lot of dragons. But for obvious reasons, he didn't have any.