The Assamites are pretty rare in the western lands, and even in Constantinople you will seldom encounter them. But if you meet one of them, it's possibly a Vizir, the face the clan presents to the outside.
The Three Branches of the Assamites
The clan presents and sees itself as judges of the cainite society. To make this organization and cause happen, they comprise three different branches, or sects, within the clan. Besides their different tasks, they also use different disciplines as in-clan disciplines. Please remember, that these disciplines are exclusive to the respective branch, and you will never find them outside the clan, except someone commited Amaranth to an Assamite.
The Sorcerers are responsible for the communication within the clan, as well as for providing for clan members while they reside in Alamut. Sorcerers use Assamite Blood Sorcery, Auspex, and Presence as in-clan disciplines.
The Warriors are the judges of the Assamites, dealing punishment when necessary. If you want to play an Assamite Warrior, your in-clan disciplines are Auspex, Quietus Crucius, and Presence.
The Assamites you are most likely to encounter outside of Alamut are Viziers. They are the public face of the clan, gathering information and keep their clan up to date with current politics and affairs. Viziers use Auspex, Quietus Hematus, and Presence as their in-clan disciplines.
Assamites are obsessed with their highest intellectual or creative ability, which acts and shows as a derangement. Additionally, the judges darken with time, which is a slow process and takes centuries.
For additional information, consult the Vampire: The Dark Ages 20th Anniversary Edition Core Rulebook on page 42f.