I've been thinking about this exact topic for a little while for a sharpening video I'm going to do. How do you tell a beginner how to detect a burr if they have never felt, seen, or otherwise detected one? Ken's basic idea seems to be the best one: Generate a GIANT burr on something you don't care anything about; that way it's obvious.
When I taught a sharpening class a few years ago I had one of the more energetic students take an old machete blade outside to the sidewalk and "sharpen" one side until he got a burr. It make a very obvious burr that just about anyone could detect. It stopped fingernail as it was dragged down the body of the blade towards the edge.
In fact that fingernail technique has become my go to technique when using coarse stones: Slide your thumbnail down the body of the blade *towards* the edge, as if your nail should slip harmlessly off the edge. On spots of the edge that have no burr, your fingernail *will* slide off. But when you generate a big-ish burr, your fingernail will catch on it and stop. The first time I felt this it was amazing. On some blades (usually VERY dull ones) I have a hard time feeling the burr with just my finger pads. I think, "Well, that feels kinda sticky, draggy, sharpish, but is it a burr? Maybe this steel just doesn't form burrs that you can feel." When I think this, it almost always means I simply have not ground off enough metal to form a burr. If I keep going, I always get one. I have yet to find a blade that I can't generate a burr that I can feel with my thumbnail drag test, at least when using a coarse stone, which is the most important in my opinion.
With that in mind, how about a $1 knife from the dollar store, thrift store, etc and some sidewalk sharpening time?
I'm actually serious. If you do this, you're pretty much guaranteed to form a big, nasty, easy to detect burr. Use the thumbnail test. Use the finger pads test. Use the paper towel test. Once you're sure you've got a burr, then you'll be able to use these tests to see what a burr actually feels and looks like. Good luck.