Tinkers' Court is located within Gnomeregan, and lies beyond the dark iron-filled tunnels leading from the Launch Bay's and Engineering Labs' lower levels. It is the location of and his minions, and is the last room of the dungeon.
If the players have come through the backdoor using the , they will have come through the Engineering Labs on their way to Tinkers' Court, and should then proceed to the Launch Bay if they want to kill all the dungeon's bosses. If the players accessed it from the front, they might have not yet done the Engineering Labs and the boss there.
This was probably where and other previous High Tinkers held court.