So 30 days it takes for Dungeon to respawn, but what about named bosses like Potema? Like there was a whole quest that i did and killed her, will she respawned too?

Named bosses don't respawn. In the Potema dungeon, you'll find an umnamed high level enemy in her place on a return visit. Likewise, any of the Galdur Amulet quests, you'll just find a high level Dragur.

If they have a unique name, they do not respawn, if they have a generic name, they can respawn. As stated above, unique named NPCs can be replaced by generic NPCs in dungeons.