The North Common Hall is located OUTSIDE Uldaman, in the cave leading up to the instance portal. Head into the cave entrance, past the tunnel leading from the Excavation Center. It is found east of Dig One and west of The Sealed Hall, and is the location of the chest needed for the quest  [43] Reclaimed Treasures (Alliance).

v • d • e Subzones of Uldaman Chamber of Khaz'mul · Dig One · Dig Two · Dig Three · Excavation Center · Echomok Cavern · Hall of the Crafters · Hall of the Keepers · Khaz'goroth's Seat · Map Chamber · North Common Hall · The Sealed Hall · South Common Hall · The Stone Vault · Temple Hall