Depending on the depth of scoring into the metal, polishing, regrinding on a belt, hand filing and refinishing, or buying a completely new one.
All knives get scratched up, and some prefer the look, as it shows actual use. Others don't want any marks at all, and leave them in their sock drawer in the box, or even in a safe.
Commonly, a 3M brown grit pad will bring them back to a 600 finish by rubbing the length of the blade. If the scratch is really deep, it will still show, but at least the surface is grained the same and it shows less. Simichrome or other metal polishes will sometimes work them out if the blade was mirror polished to begin with, like Swiss Army Knives.
What kind of knife, and how deep are the scratches?