Humans appear to have varying positions - sometimes they have them, sometimes they don't. Same goes for Goblins who I'll also touch on.
Leaders are usually monarchs (King or Queen,) or alternatively the Law-Giver. The positions may or may not be hereditary, more intensive investigation needed there, probably with Legends viewer to determine the relations between human rulers. Goblin equivalents would be their Masters, either a demon or whoever managed to depose or replace him following his or her death.
Lesser nobles will almost without fail be Lords and Ladies if they have lesser nobles, and these positions appear to be hereditary (It's not unusual for human residents to suddenly assume the position of Lord of some human site or another in a dwarven Fortress during gameplay.) They have no actual room requirements by the look of things. Goblins might also have these lesser nobles, but it seems to be less often than Humans.
Military command rests in either a Warlord or General. Functionally the same, but I've seen both, though never in the same civ. Varies from civ to civ what the position will be named between these two. Goblins also sometimes have a General or Warlord in addition to their Masters.
There's also of course various religious leaders, but they aren't civ-level nobles.
They don't seem to have any other positions - no diplomats because the leader acts in this capacity, no mayors, no militia commanders, law enforcement, or anything. This is likely because they are, without modding, unplayable outside adventure mode.