Sorry, but I can not find it
The job is on the Cape Town Quest Board with this tag: "急募!モデル募集!" It should be the third one one the board, and requires the Black Bikini.
After you do that one, another job will pop up below it (also requiring the Black Bikini. After that jobs is done, another will pop up below it (This requires the V-suit). THEN after that one is another quest below the V-Suit one - the final Quest. After you accept this quest (there is no option but to accept it once you start reading the details), go to the barricaded down steps (which lead to the other underground waterway) that is to the left / east of your home in Cape Town.
Okay, finished all the Madness Quests. Drawback to Marakef Town once you are on the Madness Questline - you can never leave, not even by teleport - AND there is no recollection room. In order to access the recollection room, you have to do one of the ending quests in the Madness Route - there are several ending quests and I'm being specific to not spoil anything here - and after the credits you will have two options.
Warning: I recommend you choose the first option until you are sure that there are no more quests to do in Makaref to prevent you from having to go through all the stuff all over again to get the rest of the quests.
The first choice will return you to the point just before you initiated the end quest. The second choice will restart the game at the beginning with all the achievements and scenes rolled over for you to watch.
Also: The naked option you receive after going full mad is in the settings portion of the Main Menu, just above the back option on the list. This option is an armor break, and to wear other clothing you have to repair it.
Bonus tip: When your desire (the heart icon in your main menu) is 100 and you're naked you have different reactions to the ero enemies (Heart alert icons) AND there are certain scenes you can perform in some of the cities. Once you've been raped by an ero enemy or performed a sex scene, your desire will return to 0.
I've seen only one ero enemy that will KILL YOU when he rapes you (You have a Bad End screen). He's just north of Makaref Slum town and also in the area just to the east of Makaref . . .1 (I think).
You can get purple ero potions from some of the item shops for 1000G that will instantly bring your desire to 100 if you are having trouble.
For the folks that are asking about getting the lewd route, KillerDxD has provided you with a save that take out most of the footwork (getting all the costumes). I'll consolidate how to get it but will not offer a save so you can jump to this. I do not take ANY credit in this because the ones before me figured out how exactly to get the Elite Route.
1) You MUST be on the Elite Route by:
a) Buy the supreme flower art 至高のフラワーアート from the flower art vendor in Free City El Chante 自由都市 エルシャンテ in Belfast ベルファスト地方 for the second competition entry requirements. It is the one that costs 10,000G
b) Collect the Belfast soil ベルファスト産用土 from a chest in Belfast region 8 ベルファスト地方 8 .
2) You must NOT have had your clothes destroyed by ero enemies during battle. Not sure if partial clothing damage from the ero enemies count, but with KillerDxD's save (the one on THIS FORUM THREAD PAGE TWO labeled Save18.txt - change the text file type to .rvdata2) will make you nearly invicible and able to escape any battle.
3) You must have followed the photo session questline from the quest board in Cape Town 辺境国家 ケープランド to its finish. This includes you getting revenge on the photographer.
a) The starting quest for the photographer line on the quest board in Cape Town is 急募!モデル募集!!and the others will appear below this one with each quest you complete.
4) You must have followed the main quest up to the part where you are ordered to get a Copper Flame Stone from Poor Town in Makaref 貧困街 マカレフ for the 4th competition.