To answer your question regarding the rear sets, usually a low and forward position of the pegs puts your knee further from the ground. Think less bend of the knee. Pegs high and back would, depending on the bike and rider's body shape, put the knee closer to the ground for a similar position on the bike as it is bent more. Too much can be uncomfortable though. An extreme example of this position would be a GP bike such as a 125 GP, Moriwaki, or 250 GP bike, all of which I have ridden.
Poor fitting leathers that inhibit range of motion make knee dragging very difficult or uncomfortable.
Dragging a knee is like a cat using his whiskers to feel his way through tight/dark spaces, or Olympic short track skaters gliding their fingers across the ice in the corners. It can inspire confidence to have the knee skip here and there, but leaving it down to grind away does not serve much of a purpose.
Good corners to practice are medium speed sweeping "carousel" type turns, though others have success in all sorts of turns.