How does Boss-Loot in Elder scrolls online work?
I'm gonna give my answer based off of experience.
Each boss or dungeon (not sure) has unique items, how many unique items I couldn't tell you, that drop from bosses. They also drop the generic gear, for example "Leather belt of stamina". You are not always garunteed to get good items from a boss.
I have gotten everything from nothing from an entire dungeon to a couple epics in a dungeon, it is purely luck.
Also something to note, every elite boss in ESO has a unique item. Atleast that I have come across.