Where to find the parking coordinates of the aircraft in the Apron?
The airport charts usually contain the coordinates of all parking positions. The charts that are available from the FAA AIP (e.g. here for JFK) only contain a single ground chart with the airport diagram:



These do not include the coordinates. But my Jeppesen charts contain coordinates for all parking positions. E.g. some gates at JFK:



They can either be found in dedicated charts for airports with many gates (like JFK shown above), or they are included on the airport overview chart for smaller airports with fewer gates.

Aircraft navigation databases also typically include the positions, so the Inertial Navigation can be initialized with a position based on airport code and parking position.

As far as I know, there is no free resource that would list the coordinates though.