It looks very similar overall to the Black Empire illustration we had from Chronicle.
Lots of obelisks, some floating, pyramids, etc. The one in Warbringers has more of a mazelike structure to it, but...
I don't know. It's hard to say he was showing her a present location. It may simply be a vision of his domain of the Black Empire as it appeared during his reign.
Also worth noting that his appearance really doesn't resemble N'Zoth as depicted in Hearthstone or in the illumination in Chronicle Vol. 3. Not that you can clearly make out many details, but its main mass appears much more spherical, like C'Thun or Yog-Sarron, while in the previous depictions it's more lightbulb shaped, like an octopus.