Make Mob Spawn Command

On my server I am adding NPCs that talk to you in the dungeons, and I have it so the dungeon closes off when the first boss is slain so no other players can join in. It sets up a wall of fences after the first mob is slain. I want to make it so if all of the players die in the dungeon or leave the dungeon then the NPC to start the quest will respawn in the exact same spot.

Is there a way to summon mobs in a exact x,y,z coordinate with the ~onDeath trigger?

Thanks in advance