Should I use "er/var/vil være" or "har/havde/vil have" before "gået"?
Thank you in advance.
Depends on context.
Usually you use 'er/var/vil være' when you the sentence describe a transition/movement in place, time or otherwise and 'har/havde/vil have' when the verbs describe a state.
Han er blevet syg - he has taken ill (transition)
Han har været syg - ha has been ill (state)
Since 'at gå' usually describes movement, most often you would use 'være'
For instance, Han er gået ud - he has gone out (transition/movement)
BUT. When the verb takes takes an object, you use 'have'
Jeg har gået en tur - I have taken a walk.
Since it can be difficult to distinguish between objects and adverbials, often 'have' and 'være' can be used interchangeably.
Han er gået sin vej / Han har gået sin vej - he has gone [his way]. Both are used