I believe potency works as a multiplier of Weapon Damage * Potency.
i.e, 50 potency and you have 10 damage (after stats) is 50 damage. But, that's calculation I don't know. I just heard potency is times that number.

The information you seek wont be given in game, you'll have to do some researching... or googling.

Though for Mage's Ballad I always thought it was static numbers. Regardless what it is, use it lol! it helps.