Detect inside Collision 2D

Dear All,

My Name is Adit, this is my first time i create a game, and i decide to use unity,

i want to create a simple puzzle games, the main idea is there is a puzzle pieces and there is a coloumn puzzle and user need to drag the puzzle pieces into the right puzzle coloumn

after wasting much time finally i can drag my puzzle pieces, but i don't know how to detect collision inside my puzzle coloumn

here i attach my source

     private var screenPoint: Vector3;
     private var offset: Vector3;
     private var curScreenPoint : Vector3;
     private var curPosition : Vector3;
     private var state : String;
     private var mousePosition : Vector3;
     private var v : Vector2;
     private var col : Collider2D[];
     var otherScale: Vector3;
      
     function Start () {
     }
      
     function Update () {
         var DragPiece : GameObject;
     
         if(state == "STATE_DRAG_PUZZLE_PIECE"){
     
             
     
         }
     }
      
     function OnMouseDown () {
         screenPoint = Camera.main.WorldToScreenPoint(gameObject.transform.position);
         offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
         Screen.showCursor = false;
         state = "STATE_DRAG_PUZZLE_DOWN";
     }
      
     function OnMouseDrag() { 
         curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
         curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;
         transform.position = curPosition;
         state = "STATE_DRAG_PUZZLE_PIECE";
     }
      
     function OnMouseUp(){
             Screen.showCursor = true;
             state = "STATE_DRAG_PUZZLE_UP";
     }
      
     function OnTriggerEnter(col:Collider){
       otherScale = col.transform.lossyScale;
       print("scale tetangga :"+otherScale);
     }
     
     function OnCollisionEnter2D(coll: Collision2D)
     {
         if(coll.gameObject.tag.Equals("kentang_kolom")) {
             Destroy(coll.gameObject);
             print("nabrak kolom kentang");
         }    
     }

any idea or comment would be very helpfull for me thanks, best regards,

aditya eka putra (@abang_adit)