i knocked the rear driver side wheel off my boxster 1999 porsche is this able to be fixed

From your brief description, it's completely impossible to tell. That depends on the damage to the subframe, chassis, suspension etc. How fast were you going, what did you hit, how much energy was pushed through the suspension into the car etc etc etc? Try posting pics of the damage and the value of the car in your country. In some countries, a 99 Boxster S is worth $50k. In others, a 99 Boxster 2.5 is worth $5k.