There is no such get function.
You'd have to click an object--such as covering your layout with a grid of small invisible buttons where each button passes its coordinates as a script parameter or you have a grid of fields and an OnObjectEnter trigger does the same....
Ironically, in FileMaker Go, you could use the new OnGestureTap trigger for this.
I am actually trying to develop this function for an iPad App so will check out the OnGestureTap trigger.
There are some associated get functions for this trigger that you can look up in help. They should include the coordinates of the tap gesture.