As I recall the low side service port for the A/C on your 1995 Pontiac Grand Prix should be located under the air cleaner housing. The air cleaner housing may need to be removed in order to access the low side A/C service port.
I have a 95 Grand Am SE and had a devil of a time as well. the location is in the middle of the car near the bottom. center engine about 3 inches on the other side of the radiator. I had a hard time finding it due to wire sheath blocking the view from the top. looks like the only way to recharge is to lay down near the front and reach underneath the radiator to unscrew the cap. my concern now is the dirty wire sheaths in really close proximity to the low port. it is really dirty around there and if any gets in it could ruin the system and it is big time dirty around it.