The sole reference to this torture comes from the Poe Dameron: Flight Log in-universe scrapbook. Nothing else is known of these procedures, other than that they were applied by the interrogation droid that was tasked with interrogating Poe and that procedure K8-04 apparently involves some kind of shock (possibly electrical in nature) applied to the victim's nervous system.
The IT unit proceeded to apply methods 2265, 6304. 3333, and
KB-A4 to the prisoner. The prisoner reacted violently to procedure
KB-A4 and nearly swallowed his tongue. The IT unit increased the
neuroshock amplitude and repeated the question: Where is the
map to Luke Sky walker?
Interestingly, in the Force Awakens novelisation, the main torture he suffered was at the hands of his captors, in the form of punishment beatings.
So sunk was he in depression that he scarcely reacted when they beat
him. Delivered with practiced skill, designed to hurt but not result
in permanent damage, the blows fell intermittently, at different times
of the day on different parts of his body. He did his best to shut out
the pain, much as he succeeded in shutting out the questions. What he
did not know was that they were merely a softening-up, an introduction
to his principal interrogator.