I disagree, but I've said all I intend to, so I'm dropping it.
Again, incorrect. It gives a condition to activate the ability, when you make a Psychic Strike. It never states that it affects the target of the Psychic Strike. Try again.
/sigh.
Here is the point: Go read Psychic Strike.
The target is your own mind blade. < You see that punctuation mark, that's a freaking period.
You coat the blade with extra energy, then, when you hit someone, that energy discharges. Psychic Strike normally just deals extra damage.
Knife to the Soul allows you to change how you charge it so that you can deal a different type of damage. It affects the Psychic Strike ability, which has no target, it is a "charging mah lazorz" ability, and KttS changes what you are charging it to do.
While that is obviously the intent, that's not what the effect says. It says, when he executes a psychic strike(Condition), he he can choose to substitute Intelligence, Wisdom, or Charisma damage (his choice) for extra dice of damage. For each die of extra damage he gives up, he deals 1 point of damage to the ability score he chooses(Effect). A soulknife can combine extra dice of damage and ability damage in any combination.
Note that the target is unspecified. Now, it obviously means that he can do stat damage to the target of the Psychic Strike. That's just simply not what it says. It does not say that the target of the psychic strike is the target, so, by the rules as written, it does not have a target. It simply does not work.