I cant seem to find the kao toun dungean in the underdark
is it not there? where on the map is it
I gave the dragon her eggs back after i let the demon eat them; i know there is a way to get out of the underdark without the dragon because she said so when i played through the game the good way; the only route i can think of is the kao toun one which i couldnt find the exit to

Look in the north west of the map near the entrance to the snirflig(?) area. Its just past the area where the myconoid king is.

Yes, you can leave via the Kua-Toa caverns. They are on the extreme right of the map, roughly in the middle, below the bridge to the Svirfnelbin(?). The exit is guarded by drow who you can bribe, offer the highest bid. Then blackmail them to open the gate out. If you fight them, then you can't leave that way.