I've a setup where player is informed by debug, triggered by selftriggerbox, that if they harvest a particular plant it will quench their thirst. The event is triggered near to one of these plants but what I want is that when the debug appears an alias target points to the nearby plant. This I can accomplish through a short quest which is triggered by the triggerbox and I can incorporate the debug message into a quest objective - so what do I need? I need to know what event is called or what event to call to register that the plant has been harvested. I only want it to happen once on this one plant not on all of them. Advice please.

Place the ObjectReference (the plant) in a ReferenceAlias that has a script attached to it. Said script should contain the OnActivate event, which can be used to advance the quest.