Questions about the gameplay of Heroes 6.

I have a lot of experience where one hero transfers about 22 skill points to another in one go. :)

Could you please elaborate on this?
1. Does the "training" skill need to be present on both heroes, or is it enough for only one of them to have it?
2. What does it mean that skill points are transferred? Does it mean that if one hero has 5 skill points and transfers them to another, they are left with 0?
3. Are skill points transferred only when the skill has not yet been learned, or does it not matter?

Added after 3 minutes

Each level increase gives one skill point. It was the same before, nothing new.

The new thing is that in Heroes of Might and Magic V, I could choose, for example, Dark Magic and learn a lot of spells, but here it turns out that one level is required for one spell.