Hey, I don’t know if I can be much help but I can try.
The way I would do it in theory is;
Have an AI Parent class (ENEMY) that has an event to cast a value (the value being the exp, maybe have some math to vary the exp gain a little) to the player, I’d then bind the Exp event to an actor destroyed event so that now when ever the AI (Enemy) has been destroyed it will cast the Exp value to the player, then I would get the player to store this and add it to his current exp, then I would have triggers to occur when you get to the certain exp value, these triggers would be the leveling up