I need to write code that returns the geographical coordinates of the location on the map where the mouse is clicked v100
You can try something like this:
myMapView.GeoViewTapped += myView_GeoViewTapped;
GeoViewInputEventArgs also have a 'Location" property already converted to map coordinates, so you don't need to do the ScreenToLocation call, simplifying the first two lines:
MapPoint p1 = e.Location;
Retrieving data ...