wiper switch

mine either had a small alan set screw that went into the side of the knob (hard to see it if it is there) or it had a little triangle clip that fits inside the knob and there is a ridge on the shaft....so once you push the knob on the triangle clip snaps into places around the ridge in the shaft. if thats the case then it will require some tugging to pull the knob and clip off that ridge in the shaft but should pop right off.

if you don't see a set screw than you just have to pull on the knob to remove it.