So the Soul knife rogue has a feature as follows:
After you attack with the blade, you can make a melee or ranged weapon attack with a second psychic blade as a bonus action on the same turn, provided your other hand is free to create it. The damage die of this bonus attack is 1d4, instead of 1d6.<
As is, the psychic blade is a simple melee weapon and as such qualifies as a monk weapon.
I think its fairly obvious that the original 1d6 of the blade will increase as a monk weapon would normally do, but does the bonus action damage also increase?