I think your problem is one, some or all in this list:
You don’t have an EventSystem in your scene. Unity creates one automatically when you create a Canvas.
Your EventSystem object doesn’t have a Standalone Input Module (Touch Input Module isn’t needed anymore as all is now managed by Standalone Input Module)
Your object is not inside a Canvas
Finally, rather than PointerClick, for touch devices you should use PointerDown and PointerUp