slug - which is what the SDK uses in order to send events to STATEWIZE.
The only remaining question is "What do I want to measure?"
Say you want to measure how many users converted from one event to another event. You would do so my building a simple funnel (No coding skills required!):
item-added-to-cart - as you've defined it on the planning canvas), or it can be the slug of a journey (i.e refer-a-friend-journey)