what brake fluid should I use for a 1988 pontiac bonneville sse

It is most likely DOT 3. It usually is printed on the master cylinder fill cap.

For fluid volume, if you have no info from the car's manual or a quick internet search, Just fill the reservoir and pump the brakes until you feel resistance in the brakes and the fluid level starts to hold in the reservoir. Then go to the right rear brake and open the bleeder valve (it should be the furthest from your reservoir). After you get a solid stream there, close the valve and go to the other rear wheel and repeat this process, then the front side away from the reservoir, then the last wheel. When done, let the fluid settle in the lines for about a half hour and repeat this process. Wish I could tell you how many quarts it will take but I would start with 2 bottles and go from there unless its a long ride to the store for more.