Outdoor knives can be sharpened on oil stones or water stones. The bevel angles chosen would be dictated by the intended use of the knife
If a belt knife is for general purpose use in camping, it should have quite a sturdy edge for making kindling, cutting rope, whittling tent pegs, and so on. The included angle of the two bevels should be at least 25° and preferable 30°. If the knife were to be used only for skinning and filleting, a 15° included angle would be ample. In both these cases, the sharpening process described for kitchen knives would be followed, but with the additional step of stropping the edge on a leather or wooden hone charged with chromium oxide. You do not need a toothed edge, so you can hone to maximum keenness.
The same general principles apply to pocket knives. The only difference is that if you have a pocket knife with two or more blades, you can sharpen the blades for different purposes.
As a matter of historical interest, traditionally pocket knives were sturdy utility knives with one or more blades pinned at one end of the haft. Pen-knives were much more refined, with very keen, hard steel blades (to shape pin nibs on goose quills) pinned at opposite ends of the haft. This distinction has now been lost, as evidenced by the photo at right above.