The Missing Brother - Act 2 Side Quest

Start Location: Memphis
Quest Location: Giza Plateau
Objective: Defeat Hesy-su-neb-ef inside the cave found in Giza Plateau

The Missing Brother Side Quest begins by speaking with Tathari in the city of Memphis; you can find her right next to the portal in the center of town. For this quest you'll need to travel to the Giza Plateau, due east of the portal in the northern portion of the zone you'll find a Cave Entrance (pictured on my map below) which is where this quest takes place.

Inside of the tomb you'll find Unas, the missing brother. He's standing outside of a closed door which will lead you to Hesy-su-neb-ef, a quest enemy which is guarding a Majestic Chest. You will need to defeat this mini boss in order to complete the quest, after return to Tathari in Memphis to turn the quest in and receive your reward.

Hesy-su-neb-ef for The Missing Brother Side Quest.