Vpetrell - are you looking at a modern reproduction version or an original WW2 version?
Re: the WW2 versions::
The only ones that had screw-on pommels were the first 50K or so made by Camillus and delivered in February 1943. The screwed on pommels were held tight with a small split nut.
After that they were either peened on or pinned.
The peened version came in 2 flavors - a round peen or a square, sometimes almost rectangular peen. Round was first. followed by square. The peened versions had 3/8" thick pommels, similar to the pinned reproductions of today. To remove the pommel on these, get or make a split nut wrench, loosen and remove the nut and then unscrew the pommel.
Next came the "thin" or 1/4" pommels that were pinned through the pommel and tang. The pin on the original WW2 versions shows on both sided.
If you are trying to remove the pommel of a peened version, you will need to grind down the peen to a flat surface and the pommel should then "pop off" with some effort.
For the pinned WW2 versions, cut a 1/2" wide x 1/2" deep dado in a chunk of 2x4, center the pin over the dado cut and use a hammer and small metal punch to "force" the pin out the other side. Once it has been exposed on the bottom side, grip the exposed pin with a pair of pliers and pull it on out. Some twisting of the pin might be necessary.
The modern reproductions have the thick, 3/8" pommels but they are pinned on and the pin only shows on one side. Called a blind pin. To remove these pommels, clamp the knife securely in a vise and use a drill with a small bit to "spin the pin" by trying to drill it out. The bit will catch in the softer metal of the pin and spin it loose.
Replacement pins are available through customer service at Kabar.com. They also sell replacement washer sets, guards and pommels if you have any of those screwed up that need replacement.
As with all work with blades, make sure the edge of the knife is safe at all times (a couple of layers of duct tape will suffice). Never hold a knife while applying a drill (or any other power tool). The flying propeller of death is fun only in Bugs Bunny and Tom&Jerry cartoons.
For the non-reproduction versions made during and after VN, i.e., Connetta, Camillus, Utica, Ontario, the pommels are also held in place with a through pin and are removed in the same manner as the Kabar WW2s