AFAIK, the Surface does not have built-in GPS.
iFly is most useful in flight when paired with an ADSB receiver. The cheapest option is a DIY Stratux kit, but you can also buy pre-assembled versions for not much more, including from the iFly store. All ADSB receivers support GPS, and iFly will prefer the GPS data from an ADSB receiver over the native GPS of the device it's running on.
If the cost of an ADSB receiver is prohibitive to you, I know there are GPS receivers you can plug into a laptop, but Google would be your friend there. That's not a very common setup among iFly users. (Honestly, I'd suggest buying a less expensive tablet and an ADSB receiver--the benefit you get from ADSB is very significant.)