I made a puzzle that closes a door, but I can't find anything anywhere to have that (door opening, or Xmarker activating) complete a quest objective.

I have an alias pointing at the Xmarker in the puzzle right now, but that des nothing but tell the player where they need to go.

you have to put getowningquest().SetObjectiveDisplayed X onto the activator object script.

this is on creationkit.com in the quest tutorial, theres similar scripting that can be done to actually set the objective and complete the objective

This requires a custom script? Activators don't have any place for script fragments.

You should be able to go the activator (the specific ObjectReference) your placed in the world/dungeon/whatever and place it there.

So, this would be:

Event OnActivate(ObjectReference akActionRef)getowningquest().SetObjectiveDisplayed 20EndEvent

As a new ObjectReference script in the Xmarker?

yes,

and you can also add GetOwningQuest().SetObjectiveCompleted 10 ; to end the first objective in that same script

You can also add a GetOwningQuest().SetStage 20 as well ; might be SetStage(20) beenawhile sry

edit: actually i think you have to put the variables, ie 20 in () parantheses. like ^ above example, on all of them