public GraphicRaycaster m_CanvasUI;
    public EventSystem eventSystem;

     private void Update()
    {
        if (Input.GetMouseButtonDown(0)) {
            CheckSecondUI(Input.mousePosition);
        }
     }

    /// <summary>
    /// 檢測是否有第二層UI
    /// </summary>
    /// <returns></returns>
 

    public void CheckSecondUI(Vector2 pos)
    {
        List<GameObject> objList = new List<GameObject>();
        PointerEventData eventData = new PointerEventData(eventSystem);
        eventData.pressPosition = pos;
        eventData.position = pos;

        List<RaycastResult> list = new
 
 List<RaycastResult>();
        CanvasUI.Raycast(eventData, list);
        if (list.Count > 0)
        {
            for (int i = 0; i < list.Count; i++)
            {
                Debug.Log(list[i].gameObject.name);
            }
        }
        else {
            Debug.Log("沒有UI");
        }
    }
 

當滑鼠在螢幕上點選時，會打印出滑鼠下所有的UI物體的名稱