2001 Pontiac Grand Prix Spark plugs

There's a number of variables to what you're asking for. The best place to look is at the emissions sticker under the hood. That will list the spark plug number and gap. For spark plug wires, any auto parts store will have the right ones for your application.

The Check Engine light means the Engine Computer detected a problem, set a diagnostic fault code, and turned the light on because that code relates to something that could adversely affect emissions. Obviously rough running, (a misfire), and poor fuel mileage means increased emissions. Many auto parts stores will read those codes for you for free, but be aware that fault codes never say to replace parts or that they're defective. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. In this case there will hopefully be one or more codes telling you which cylinders are misfiring.