If you kill the Group Boss in a Public Dungeon then you get Undaunted Exp. This is the boss that also gives you a skill point. But the other bosses and mobs in a Public Dungeon do not give Undaunted Credit. Other than contributing to the Damage Dealer/Healer/Block achievements which do give you undaunted credit.
Is this repeatable? Or are you referring to the achievement points you get for completing the Dungeon after killing the main boss in a Public Dungeon?