This is a question that comes up a lot. First, the overwhelming difference between ceramic knives and steel knives is, ceramic knives stay sharp almost indefinitely. You might ask how is this possible. Well, ceramic knives are manufactured from Zirconium oxide one of the hardest materials on the planet and rivaled only by diamonds for hardness. When a steel knife dulls the edge rolls and when you re-sharpen it you are straightening the edge. Zirconium does not roll which gives it its edge retention properties.
However should you feel your ceramic knife does require attention you should not use a standard sharpening device as they are not aggressive enough to properly restore the edge. Both Stone River Gear and Kyocera offer complimentary re-sharpening services and you can contact them directly if you would like them to put the edge back on their respective brands.
However if you do prefer to do it yourself, Chef’s Choice from Edgecraft provides an excellent electric sharpener that does both Ceramic and Steel blades.