How do you sharpen an s-grind knife? Just like a regular flat grind knife! Below the hollow and just above the edge the blade is essentially a flat grind blade, so sharpening is no different than that for a regular knife.
I sharpen each of my knives using a 600x CBN wheel, followed by a leather wheel to strop to a mirror polish, both installed on a slow speed grinder similar to the Tormek Sharpening System. I am very happy with the edge I achieve with this setup, and have yet to hear any complaints with the out-of-the-box sharpness! Although it is expensive, the speed with which I can sharpen outweighs the cost, since I do sharpen a number of knives each month!
For most home chefs, I recommend a ceramic or diamond honing rod—something in the 400-1000x range. They are similar to the old style steels, but harder and cut more evenly on the harder knife steel. I touch up my knives as needed—this simple maintenance lasts quite some time before I need to head back to the wheel.
Honing rods are inexpensive and, in my opinion, do a great job! They are quick, easy, and cost-efficient, making it a welcome alternative to the significant time investment of getting stones set up when you are just trying to cook dinner!
Another option is water or diamond stones. While very versatile and the best way to sharpen, learning this technique requires a considerable time investment—you’re bound to scratch a lot of knives as you learn the ropes, so if you decide to go this way I suggest you start with some beater knives!
A good alternative to the stones is the Lansky System—while not the fastest method, it is very easy and provides consistent results! I started out with this technique and recommend it as a first system, done in conjunction with a ceramic or diamond hone for touch ups in the kitchen. I also recommend a leather or denim strop for final honing—you can easily make your own with an old leather belt, or scraps of denim glued to a board. There are also many good commercial options out there—I have plans to debut one in the near future, so stay tuned!
I would avoid electric and non-electric pull-through sharpeners at all costs! They can ruin the temper in the knife, remove much more material than necessary, and scratch the edge of the knife, causing irreparable damage to your knife.