looking down at the face of the dog clutch you will see three "dogs. These mate with three dogs on the forward (and reverse) gear, depending upon which gear you select. The face, that is, mating surfaces, of the dogs will be vertical and when new there will be a sharp right angle. The drive dogs are tapered on the rear to ease engagement and that lower surface is NOT the mating face. When worn, the face will be rounded.
Since the faces of the dogs wear evenly, you simply need to hold the Dremel vertical to it and slowly, with a steady hand, grind back until you have a vertical face with a sharp 90 degree angle. NOW: Since the drive dogs on the gears will also wear, it is almost useless to grind the dog clutch faces without also grinding the mating dogs on the gear.