How can I tell my laser which enemy to target?

Create new parameter ("ID", for example) in gameObject and laser In spawner object before instantiates new object set each time new ID (just increment it). Then in laser script check ID of laser and gameObject, if it equals - track, if not - dont track.

 // gameObj script
 
 public var ID : int;
 
 // ur code here

 // spawner object script
 
 public var Prefab : GameObject;
 public var PrefScr : NameOfPrefabScript; // name of script with id attached to prefab
 public var action : bool; // trigger
 public var ID : int;
 
 function Start () {
    PrefScr = Prefab.GetComponent(NameOfPrefabScript);
 
 function Update () {
    if (action){ // if trigger set on
       PrefScr.ID = ID;
       Instantiate (Prefab, transform.position, transform.rotation);
       ID++;
       action = false; // set trigger off
    }
 }


 // laser object script. i dont know how u create laser for new game objects, get ID like in gameObj/spawner for this too.
 
 public var ID : int;
 public var parent : GameObject;
 public var parentScr : NameOfPrefabScript;
 
 function Start () {
    parentScr = parent.GetComponent(NameOfPrefabScript);
 
 function Update () {
    if (ID == parentScr.ID){
        // do what u want, track position and etc.
    }
 }

Could you tell us what you are trying to achieve ?