Where can I find the fuel cutoff switch for a 95 g20 mark III relay and fuse are good tested the pump but still no fuel pressure

Ford is the only one I know of that uses a cutoff switch. GM use a relay usually in the under hood fuse box. Try opening gas cap & have someone put their ear to it, turn key on without starting, they should hear fuel pump hum for a few seconds, meaning it's working. If not check for blown fuse or bad relay, if you find something wrong with fuse or relay, replace it, & do the test again, if still no hum at the pump, it's likely pump is bad or you have a bad connection or bad ground.

Try crankshaft positioner. It needs to accurately report rpm to the ecm to kick up fuel pressure. Check Inertia switch for fuel cutoff and reset.

What about the fuel pump relay and the oil pressure loss fuel pump cutoff switch?

It is located in the relay and Maxi fuse box under the hood near the battery, both the fuel pump fuse and relay are in this box, the fuel pump fuse is a 20Amp and is marked #10, the fuel pump relay is is marked as relay #301.

There is also a fuel pump cutoff switch (triggered by an accident exceeding 3 G's)

The fuel pump shut-off switch is

located in the passenger's foot well,
by the kick panel.

make sure of connection of fuel pump ,and check by ignition if it works or not.

Here are some troubleshooting ideas--let me know if you have more questions.
In most modern cars, the fuel pump is inside the gas tank and is also usually sold with the fuel gage sending unit--an expensive and laborious R&R job. If the pump is working, you should hear it at least momentarily when the key is turned to the "on" position. If the pump is not working, the cause could be a fuse, a relay, an accident "kill" switch that needs resetting, or the pump itself. You'll want to rule out all of the inexpensive possibilities first. Use your owners manual (you can often find these online if you don't have the original) to locate the applicable fuse, relay, and/or cutoff switch. To check the relay and ignition switch, follow precedures at http://www.fixya.com/cars/r6022358-relay_check. You can also check for voltage at the pump connector with a test light.
Assuming your pump works, fuel still needs to get to the engine. A clogged filter will certainly limit fuel flow, but will rarely prevent a car from starting. That said, filter replacement is an inexpensive bit of maintenance. Most likely cause of fuel not getting to the engine when the pump is working is the fuel injection system (not an issue for carbureted engines). Injection systems are beyond the scope of this tip, but there are a couple things you can check. Many anti-theft systems cut off the injectors when activated. If you have such a system, make sure your anti-theft system has not been activated. Also, the injectors require a certain level of fuel pressure. Though your pump may be working, it may not be producing pressure. If possible, have your fuel pressure checked or borrow the appropriate tool to test the pressure. Always check pressure at the fuel rail, as some designs include a separate regulator that is typically in the line in the engine compartment.

I don't remember this vehicle having a cutoff switch. In that year most manufacturers that were installing cut off buttons were mounting them in or just behind the glove compartment. If the pump has stopped working check the fuses located inside and under the hood of the vehicle and check the fuel pump relay. If all are good it is most likely a bad fuel pump you will need to replace.

CHEVY DOESN'T USE A FUEL PUMP RESET/CUTOFF SWITCH, FORDS USE THIS FEATURE, ON A CHEVY IT IS DONE WITH THE OIL PRESSURE CUTOFF SWITCH, SO IF U LOOSE OIL PRESSURE THE FUEL PUMP CUTS OFF, THIS OIL PRESSURE FUEL PUMP CUTOFF SWITCH AND IT'S WIRING ARE NEAR THE OIL FUILTER UNDER THE TRUCK.

If you're car has been running fine, then suddenly won't start, the cause is frequently that the fuel pump cutoff has been tripped. Open your trunk, and look for a label for a fuel pump cutoff switch. Locate the switch, press it in, and see if the engine will start.

Did you see if the inertia switch was triggered. The emergency fuel pump cutoff switch, also known as the inertia switch, cuts power to the fuel pump in the event of an accident - even a slow speed one - any sudden "jolt" can trigger the switch. 

The switch is located inside the jack storage compartment found at the right rear of the vehicle. Remove the cover and it is behind the thin "foam" covering inside the compartment towards the rear of the vehicle. 

It has a red button on the top of the switch, make sure the button is fully depressed. If it is and the vehicle still won't start check fuel pressure at the rail (there is a port on the rail which is under the hood on the engine) with a fuel pressure gauge. If the pressure is ok (about 30 psi) the problem is most likely not fuel system related. 

Good luck and hope this helps.