The term "Zul" as a prefix is generally taken to be akin to the adjective "mighty" or "great." So Zul'jin would be "Great Jin" and Zul'Gurub would be "Great Gurub." "Jin" itself is often taken to mean "leader" or "master" - so Zul'jin's full name would be "Great Leader" or something akin to that. Zuldazar would basically be "Great Dazar," a testament to Dazar as the founder and first king of Zandalar.