Volume 2: Deep End
You need to successfully pickpocket the Elevator Key Card, from either of the 2 Head Guards wearing Orange vests, without being spotted by any other Guard.
If you follow the 1st part of the video, you will see how to pickpocket the Head Guard outside the station. However, there is a 2nd Head Guard inside; who walks between the elevator & Coffee shop, after you speak with Han-Jae.
The 2nd part of the video, shows the location of the 7 Security camaras, needed for: