The way that Grim Dawn works is that every proc happens on attack with weapon damage % unless otherwise stated. In your first example, resistances will only be reduced if your attack has % weapon damage. That means it won’t work with skills like Trozan’s. Some skills without a weapon damage component can reduce resistances, but they will explicitly state that they do in their tooltip (like Curse of Frailty, Agonizing Flames, etc). Your second example follows the same rule: it only works when you attack with weapon damage %. Some effects do indeed activate when you are attacked, but they will explicitly state that this is the case.