Well your Theory/Psuedo code is correct..It should work
A few other things to check would be Z order Make sure that you are spawning the object on the right layout and that its visibility is properly set..
Try spawning the object somewhere else first using the same code...and If it appears then its most likely just behind the Enemy1.sprite
You can add a small code directly after the spawn that is
Targeting Graphic->Move to top of layer
try that...there could be a few other problems but that is what I would try first..
its not the only way to check X though...
you could also do something like
Every Tick-> System(Compare two values)Player.X = Enemy1.X
Action->spawn Targeting Graphic at Enemy1.(image point)
hope that helps