I used a couple of those plastic levers you can get to help dismantle the dashboards etc of cars. They're very cheap - literally pennies - and are designed not to damage surrounding areas, so ideal for this job. Use two levers set at 180 degrees to each other and pry up very gradually, turning the knob a few degrees each time before applying pressure to the levers.
I needed to get the knob off so that I could spray some contact cleaner onto the dirty pot track without having to dismantle everything. Worked a treat, now noiseless and no damage whatever to the guitar.
A good, efficient, cheap fix