It seems you MUST complete the Tactics Pearl quest BEFORE you can get the cutscene from Luto actually telling you which location listed below you need to travel to. You can go to ALL of the locations and nothing will happen when you click on the ??? If this is happening to you, do the Tactics Pearl quest and then come back and talk to Luto. You should then get a cutscene exactly as listed below. (update - I have not yet finished the Tactics Pearl quest, but I WAS able to get the CS and location (Ranguemont Pass) from Luto.)
Click the ??? to spawn the Metallic Slime with about 900HP. Your NPC will appear to fight with you. Slime and NPC will immediatly engage and attack one another.
Talk to your npc and then check the ??? point again to receive the Vitrallum (key item).
Head to King Ranperre's Tomb and zone out into Jugner Forest. Head east to the lake and then north for a little bit until you find a ???. Click it for a cutscene to complete the quest. You can not reach the ??? from the main path in Jugner Forest because all paths are blocked.
Luto has asked you to locate a special metal that can be used to repair the broken mirror. According to her research, this substance can only be found inside an extremely rare species of slime.
