Where is fuel filter for 2003 grand prix 3.1 located

Under the car on the driver's side just forward of the rear wheel.

How do we no if fuel filter no good

It would show up if you did a fuel pressure test. If its really ancient it will eventually corrode and start to leak like mine did. It's something that should be changed from time to time as part of maintenance. Once every couple of years is usually plenty although your owner's manual may suggest something else. If its been on there for years it can be quite difficult to get off, so you may want to ask a shop to do it if you're not well equipped with tools and patience.