From Halopedia, the Halo wiki

Inquisitive is an achievement in Halo: The Master Chief Collection. It is awarded for activating the second Halo 2: Anniversary Terminal on Outskirts. The achievement is worth 5 Gamerscore and can be unlocked on any difficulty. The Xbox achievement art is concept art of a human mess hall/prep room, likely used for the scene in the second terminal where Thel 'Vadamee attacks the UNSC HQ on Camber.


The terminal is located inside the structure with the rocket launcher and sniper rifle ammo encountered before entering the tunnel. It is on the bottom floor inside the structure, and takes the form of a monitor flashing "INCOMING MESSAGE".