As for the
Kanji dungeon, take your save back to when he first goes missing (if you can), immediately go to the shopping district that afternoon, and speak to his mother in front of her shop. You can then go to Junes on Tuesday or Thursday (Kanji goes missing on a Mon I think), talk to Naoto, and unlock the dungeon
. If you go to GameFAQs, they have alot of guides in their Persona 4 (not
Persona 4 Golden) FAQs section, one of them is a boss guide. Good luck!