Open the panel.cfg of the aircraft that you want to copy the GPS from and cut and past the section into the aircraft that you want to add. Aircraft are located in the Simobject folder-> Airplanes Folder. Here is the GPS section from the default Cessna 172. Add the GPS title under [Window Titles] with the next number in sequence.
[Window Titles]
Window00=Main Panel
Window01=Radio Stack
Window02=GPS
[Window02]
size_mm=456,378
window_size=0.5
position=8
BACKGROUND_COLOR=0,0,0
VISIBLE=0
ident=GPS_PANEL
zorder=4
gauge00=fs9gps!gps_500, 0,0