A picture would really help. What's the handle material? Fixed blade, I take it?
Make sure it's good and dry. Don't do this on a rainy day. Depending on how small the gap is, get in there with a pin or guitar string and gently clean out any gunk. Then drizzle some super glue in the gap... it's thinner than most epoxies I know of. Push it in there with the wire or whatever to try to get it all the way down in there. You may need to repeat the glue application a couple times to completely fill the gap... let it cure up good and hard. Try not to get it all over the knife

Mask off the areas around the gap. Once the gap is filled and the glue is cured, remove the mask, get the finest sandpaper you can find, and clean off any excess.
Don't bother clamping it, it will probably just pull apart again someday down the road. Just let the super glue fill it up. It's not perfect but it will help keep gunk/moisture out of there.
Just my $.02 and worth every penny you paid for it.