Hi,
my experience from yesterday:
To learn Adrenalin, you need no point in Scoundrel. You just need a 'free' spell slot. When you learn it from eating, the spell is put into the list of usable spells (left side), and into the active spells (right side) - but just, if you have a free slot.
If you take it off from the active spells, you are not able to put it back.
So if you learn it at a point, where you have a free memory slot, you should leave it there for the rest of the game

Tarnim