Six year old chef knife handle is loosening at the bolster, can this be fixed Repair

Fixable, and it is a Saturday afternoon rather than a funeral. The rivets are almost certainly still tight; what has failed is the adhesive under the scale, which the dishwasher cooked off. Lay the knife on its side, wick thin CA glue into the gap, then clamp with two spring clamps and a strip of cardboard so you do not dent the wood. Leave it 24 hours before washing it.

If the gap will not take glue because it is full of grease and old food, flush it with acetone on a pipe cleaner and let it dry overnight first. Do it soon rather than eventually. That dark line is water sitting against carbon steel, and once it pits under the scale you cannot get at it.

The dishwasher is the whole story. Wood scales move with humidity, the detergent strips the finish, and the heated dry cycle expands the steel and the wood at different rates until the bond lets go. Twelve cycles is plenty to do it. Nothing you can undo now, but the repair holds fine if you hand wash from here.

Before you glue, put the knife in a vice by the blade and try to twist the scales. If the whole handle rocks and the rivets turn with it, you are not looking at a glue failure, you have a partial tang that is working loose in the handle block, and that is a rehandle rather than a repair. Three visible rivets usually means full tang, but some makers put decorative pins in a hidden tang handle and it is worth thirty seconds to check.

If it ever does go past saving, a rehandle is not a big job for a local knifemaker. I paid about 70 for stabilised wood scales and new pins on a knife worth maybe 120, and I would do it again because the blade was already shaped to my hand.