The submissions from GnP are contextually available. In every case you need to either have your opponent in a health event (striking in GnP can stun to get you there) or have a stamina advantage of 25. Your fighter also has to have the submission in their moveset.
From Backside Up:
RB+LT+RS Down Darce.
From Fullmount Up:
RB+LT+RS Down Armbar.
From Halfguard Up:
RB+LT+RS Down Half Guard Kneebar.
From Knee on Belly:
RB+LT+RS Left or Right (based on current side) Armbar.
RB+LT+RS Left or Right (based on current side) Crucifix Americana.
Fetal:
RB+LT+RS Left or Right (based on current side) Japanese Necktie.
RB+LT+RS Left or Right (based on current side) Sidesaddle Arm Triangle.
Stacked Guard:
RB+LT+RS Left or Right (based on current side) Stacked Guard Heel hook.
RB+LT+RS Left or Right (based on current side) Stacked Guard Kneebar.