Is KnightTurret in the same container with the Knight? If not, then the code that pins them will not work correctly.
"Acquire target" means a single target - a particular goblin instance among all other goblins. So you need to pick that instance before acquiring! Like I said, it's up to you how to pick it (by visibility, distance, lowest HP etc.), but you need conditions to pick the goblin instance. Please read some tutorials about picking in Construct, it's very important to understand how it works.
Another option is automatic targeting - use "Add object to target" action. Then turrets will automatically select the target in range. This target can be identified by UID. If you want the knight to move to it, pick the instance by UID first:
Every 0.5 seconds
For Each Knight
Goblin pick by unique ID = KnightTurret.Turret.TargetUID
-> Knight Move To Goblin