Seeking the Order is an Act 3 side quest offered by Haruuv in Homestead, after choosing to side with the Order of Death's Vigil in the Allies Among the Ashes quest.
Master Varuuk is located in the Bastion of the Order, which can be found just to the left of the Sorrow's Bastion Riftgate.
Varuuk will then offer the Worthy of the Order side quest.
|Haruuv, a representative of the Order of Death's Vigil, has asked you to travel to a crypt near Sorrow's Bastion, where the Order has its sanctum. To reach the crypt, follow the road north out of Homestead, through the Fallow Fields. When you've reached the ruins of Sorrow's Bastion, look west for the crypt entrance. Once inside, speak to Master Varuuk.