Fuel filter

Under vehicle, driver side, below seating area, front of fuel tank, mounted on chassis in fuel line here is a guide that will walk you through the service

https://www.2carpros.com/articles/how-to-change-a-fuel-filter

Please let us know if you need anything else to get the problem fixed.

Where is the fuel filter located in the engine compartment? Or is it an in the tank fuel filter?

The fuel filter is located under the car on the left side near the fuel tank here is a guide and diagrams below to help you get the filter changed out.

https://www.2carpros.com/articles/how-to-change-a-fuel-filter

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Cheers

Engine Mechanical problem
1998 Buick Regal All Wheel Drive Automatic 93000 miles

Where is the fuel filter located and how can I check to see if it needs to be replaced?

Check near the fuel tank or along the fuel rail. Fuel filters should be replaced aprox every 30K. You can check fuel pump pressure before and after the filter to know if it is plugged.