Cobra Oasis (Location)
A cobra lair in the Waset Desert.
Like most lairs, in that you need to kill the alpha-beast to complete the location.
Unlike most lairs, in that Sutekh is lying dead here (if you've completed the main quest).
The relic isn't on him, but I'm sure he had time to hide it safely in the few days since you saw him last. It's not like this is the sort of desert where someone would just rob a corpse….