I have got a 10" clown knife and we feed sinking carnivore pellets, prawns, worms and frozen lance fish also he has had mealworms in the past not a fussy eater.
blood worms and feeders( only a treat) cichlid pellets, and tro[ical fish flakes both my knife fish eat all of this stuff but they dont touch the con or the dempsy in the tank with them