How can I best select a knife to purchase for learning how to sharpen?
While you can learn how to sharpen on almost any straight blade knife, my recommendation is to start on one that:


Isn't expensive, (try yard sales, thrift stores, and pawn shops - the goal is to learn technique, not have a fancy knife)
Isn't very long, (6 inches max)
Is wide enough that wearing the blade away won't be a big issue, (chef's knife would be fine)
Is not too thin or too thick, (not a boning knife or a meat cleaver)
Is a softer typer of steel, (so that you will sharpen more frequently, and so it will be easier to grind back the edge if needed)
Doesn't have a great finish (the finish is the part that you're most likely to mess up beyond easy repair).




As far as sharpening tools go, I think you need several grades of whetstones to really get a great edge. You can buy them separately or as part of a kit. I would skip any other type of sharpener, even a honer for now (again, so that you'll be forced to practice resharpening more often).

Then it's a matter of practicing sharpening and testing the edge. Make really sure you get your technique down before trying to add ANY speed. Make sure your fingers are NEVER in the path of the blade. Work from roughest to finest whetstone.

If you mess up on the whetstone angle, go back to the roughest stone and regrind to a fresh edge.

Your practice knife will get scratched up and worn down faster than normal. When you're comfortable with your skill, get a slightly nicer knife and a honing steel.