The blade might be able to be welded. Unless it’s a rare collectable knife, the cost to do it is probably more than the knife is worth, plus the result is a cosmetic repair not a usable working blade (unless you also have the blade tempered).
Best bet is probably to replace the blade. For that you'll need an appropriate blade from a donor knife. If your next question is who to do it, go to the Knife Restoration and Repair forum here, viewforum.php?f=37
find someone whose work you like and send them a PM with pictures of your knife and a description of what you want done, and request a quote.
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