Whenever you buy a white oak jo or bokken, you should sand it lightly to remove the thin layer of varnish that is put on it, then coat it with a light oil (I use almond oil, a friend uses mineral oil) and rub it in. Do this a couple times the first day or two, then once every few months thereafter. If you don't do this, it becomes dry and brittle, and, well, it looks like your jo. Try doing this and I think you'll see some improvement. You'll have to sand a little extra to smooth out the rough spots.