To unlock the T8-NK Frame, you will need to fast travel to the Renegade Vault. The dungeon will become available after you have unlocked the AP-3 frame in the Lost Crawler and travel to another Fast Travel Point to talk to Violet. Enter the Vault and follow the objective markers to an open room with the T8-NK Frame behind a force field that requires you to find 3 Cellbots.
From where you enter the room there are platforms on the left hand side. Double jump to the first and then turn to the right to find a cavern in the back left corner of the room, inside is cellbot #1.
Go back down double jumping and dashing to get to the front left corner of the room. In the corner you will see another cavern with cellbot #2.
From this cavern dash, double jump and dash to the center platform and then dash, double jump and dash to get to the cavern where you will find cellbot#3.
Return to the center of the room and the bots will enter their sockets unlocking the force field to which will unlock the T8-NK Frame and the achievement.