It is an event: Event Blueprint Used, it is available from blueprints you child from the PrimalItem_Base blueprint. Basically, I just keep looking until I found it. So, if you base an item on it, then place it in inventory, when you select it, then press “USE ITEM” button on the main ARK Inventory screen, it will fire that event.
So, you can make a item “do something” when you click the “USE ITEM” button. Problem is that I am having a really hard time getting a reference to the Player that owns the item…