How to Event tigger when drag and drop complete

instantiate objects drag and drop system is implemented for collectibile card game …i want when drag and drop is successfull done into relevant places …some event ,(method) running

player can drag and drop what ever the card (object ) to given places …order can be vary ,but how ever the each 4 slots fill with one card event should be trigger

If you use Unity UI and an Eventsystem you could have a script on each item that implements IDropHandler and IDragHandler. Here is an example that simply drag and drop a colour.

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class MyDrag : MonoBehaviour, IDropHandler, IDragHandler
{
    Image myImage;

    void Awake()
    {
        myImage = GetComponent<Image>();
    }

    public void OnDrop(PointerEventData eventData)
    {
        if (eventData.pointerDrag != null)
        {
            myImage.color = eventData.pointerDrag.GetComponent<Image>().color;
        }
    }

    public void OnDrag(PointerEventData eventData)
    {
    }
}