The Pontiac Bonneville used the same power steering fluid from 1992 until 2005. You should look for GM Power Steering Fluid with part number1050017 for quart sizes or part number 1052884 for pint sizes.
This is two of the things I know that could be wrong. The power steering pump is either bad or there is no power steering fluid in the pump causing it to have steering problems. Be sure to check the fluid level in the power steering pump.