And I tried to use a func_lookdoor, but concole erors me with:

ERROR: DoorLook (test) given no target. Rejecting spawn.

But THere is no target thing to fill in.

What the heck is func_lockdoor?

A door that moves when either looked at, or a target object moves close to. The VDC should help both of you.

I assume the OP didn’t set a target.

And one thing lkistred there is:
* !FGD target

<target_destination> View cone switch for this door. (Necessary to trigger it.) 

But I can’t seem to add this. I already tried turning smart edit off, and just filling in this value, but it doesn;t work.

Oh, I misread it.
Can’t you use a trigger_look with outputs to open the door?

trigger look was only in singelplayer right?

I’d imagine that both trigger_look and func_lookdoor are both singleplayer entities.