The LOK Crew Capsule is an part of the LOK spacecraft, and is a part of the N1-LOK-LK and Soyuz rockets. You can also put it on an Gemini Service Module. Like the Orion, Gemini Capsule and Crew Module, It can splash down on any planet with an atmosphere.
This capsule is seen docked with the MSS in Mission 11 and Mission 19, while you need to splash down one in Mission 19. It will be unlocked in Mission 20. You need to build an N1-LOK-LK rocket with it in Mission 21.