pathfinder TWF ninja rule question

[cosmiceffect]

The ninja is able to gain an additional attack during a full attack action at his highest base attack bonus, my question is if he is duel wielding does he gain an attack for each weapon?

[FocusWolf413]

I would say only if it has enough twf feats to use it. If the ninja has a bab of +6/1 and only has one twf feat, it can only do 4/4/4/-1. There's a whole chain of feats for twf. You need one for each iterative attack.

[grarrrg]

The ninja is able to gain an additional attack during a full attack action at his highest base attack bonus, my question is if he is duel wielding does he gain an attack for each weapon?

No.
The ability says "...make one additional attack...", meaning you get one additional attack, period.
You can make the attack with any of the weapons you are using, but you only get the one.