The lab serves as Tong's research place. It is hidden behind a code-locked door in the kitchen of the Path compound, and another button-locked one which is placed as a part of the wall. The room in between is guarded by one of the Path members and has various cardboard and metal boxes, as well as a table, bird cage and a crowbar.
Inside the lab are multiple PC consoles, one of which JC uses - he's given the username and password. Another of the Path members sits here, although he's no longer a guard - instead, just a scientist. There's also a shooting range, which has a few ammunition boxes and three targets - a simple crosshair, a figure and a person holding a hostage.
If you intend on using the shooting range for whatever reason, make sure to limit yourself to silenced weapons or risk the wrath of Tong's guards.