A BGK finds it food by its electric discharges. It has special sensors that it uses to find its meals, and they are most concentrated on the dorsal side (the top of the fish). Maybe you have noticed that when your BGK does eat, it pitches its body downward so that it approaches the food with its "forehead." It also determines the location of the food by scanning past it slightly so the dorsal sensors can detect it, then quickly reversing to bring the food close to its mouth. You might try directing the food at the BGK with a turkey baster, up above its head, not right in front of its face.
You didn't mention how big your knife is, but I think 2 cubes of bloodworms per day is too much unless the other fish are eating some, too. You could thaw them in a cup and give 1/2 at a time if you want to feed twice a day. When they're thawed, you can mix them with a little tank water and squirt them near your knife with a turkey baster. If you mix in a little garlic essence (like Garlic Guard from Seachem), it might help your knife notice them more.