Which gameObject is touched when touch at overlap gameObjects?

If your cards are sorted by order in layer and are colliders you could do the following.

Get all your cards with the physics 2D cast you need for example OverlapPointAll. then sort your colliders and return the one that order in layer is the maximum.

     Collider2D GetFrontCollider(Collider2D[] colliders){
         int max = int.MinValue;
         Collider2D collider = null;
         for (int i=0; i<colliders.Length; i++) {
             SpriteRenderer spr = colliders[i].GetComponent<SpriteRenderer>();
             if(spr != null){
                 if (spr.sortingOrder > max) {
                     max = spr.sortingOrder;
                     collider = colliders [i];
                 }
             }
         }
         return collider;
     }

This should return the collider of a collider array which order in layer of the SpriteRenderer component is the maximum.

There must be a more elegant solution but this one should work though.