D&D 5E Soul Knife ability question.

[ManBagel]

At 3rd level when you adopt this archetype, you can manifest your psionic power as shimmering blades of psychic energy. When you are about to make a melee or ranged weapon attack against a creature, you can manifest a psychic blade from your free hand and make the attack with that blade. This magic blade is a simple melee weapon with the finesse and thrown properties. It has a normal range of 60 feet and no long range, and on a hit, it deals psychic damage equal to 1d6 plus the ability modifier you used for the attack roll. The blade vanishes immediately after it hits or misses its target, and it leaves no mark on its target if it deals damage.

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.

Does the second attack have you add your Dexterity Modifier?

 

[Kurotowa]

Going by the UA wording, since I get my book in two days, then I'd think you would. The general rule is that you add your attacking stat's bonus to weapon damage rolls. The specific rule on PHB p195 is that you don't get that bonus if you use the Two-Weapon Fighting option for an extra attack with your Bonus Action. But the Soulknife isn't using the TWF rules. It has its own personal option for making an attack with your Bonus Action that sidesteps the TWF rule entirely.

Psychic Blades doesn't create an off-hand weapon that requires TWF to attack with. It gives you the option for a Bonus Action attack that just so happens to require a free off-hand to make, which is similar but legally distinct from using TWF.

 

[Weiley31]

Using your mind overrides the TWF restriction.

 

[Paul Farquhar]

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.

Does the second attack have you add your Dexterity Modifier?

Yes.

The second attack is granted by a class ability, not by duel wielding.