The base Sneak Attack rule still applies

Psychic Blades qualify for Sneak Attack because they are finesse weapons. Sneak Attack can be applied to the first or bonus-action blade that hits, provided the normal qualification conditions are satisfied and Sneak Attack has not already been used that turn.

Subclass interaction

Psychic Blades qualify for Sneak Attack because they are finesse weapons. The first blade deals the larger damage die; the bonus-action blade is another opportunity to land Sneak Attack if the first attack missed and Sneak Attack has not yet been applied that turn.

Reaction attacks can still matter

The Soulknife has fewer subclass reaction demands than some Rogues, so an opportunity attack can remain a strong off-turn Sneak Attack opportunity. Psychic Veil and later psionic features mostly compete through other parts of the action economy.

Do not double-count subclass damage

The second Psychic Blade attack is not a second Sneak Attack by itself. It is another qualifying attack that can carry Sneak Attack only if the feature has not already been used on that turn.