TWIST THE KNIFE [one-action] FEAT 6 ROGUE
Requirements: Your last action was a melee Strike that dealt sneak attack damage to a flat-footed target.
After stabbing your opponent in a weak spot, you tear the wound open. You deal persistent bleed damage to the target equal to your number of sneak attack damage dice.
is this percistent damage acumulative if you can do this more times in the combat?
No, multiple sources of persistent damage do not stack if they are the same damage type.
"If you would gain more than one persistent damage condition with the same damage type, the higher amount of damage overrides the lower amount." (CRB 621: Persistent Damage Rules).
It's not, the same type of persistent damage don't stack.
That feat is basically a damage option that don't use or is affected by the multiple attack penalty.