It is on the lower left side of the engine looking from the front of the engine. There should be a cap to pull off. Do not over fill.
And its nearly impossible to find. It's at the back of the engine near the firewall on the passenger side underneath a bunch of things. You'll need a good light to see it and a funnel with a long flexible hose on it to get the fluid down there. I stuck an 18" piece of rubber tubing onto a normal funnel, but you can buy them at an auto parts store if you're not feeling creative. Its a bit of a fiddly job, but one you or a friend can easily do with a little patience.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts
Related Models For Sale
Used Cars for Sale