Knight'N Knight Research - Compiled on 1st July, 2018 by Peter O'Hanlon (Tongara).
Updated on 19th January, 2020.

Knight'N Knight is an unreleased game. It was set to be a true sequel to the Clockwork Knight series. It was mentioned to possibly be an RPG on certain websites (although this isn't 100% confirmed), and was set to be released on the Nintendo Gamecube. 12th May, 2003 is when the game is first mentioned anywhere in the press, and seemingly for the last ever time.

The game was being created by an in-house SEGA development division known as "Overworks". 
Overworks was established on 21st April, 2000. Overworks main task was to continue the Sakura Taisen series, but they also seem to have done other things such as Guru Guru Onsen and it's sequels and Skies of Arcadia: Legends.
A full list of their works can be seen at https://segaretro.org/Overworks.

On 1st October, 2003, the division was made defunct and merged with a development company owned by Sega Corporation known as "WOW Entertainment ", becoming Sega WOW (briefly "WOW Works") on the same day. It is possible that this series of events lead to the games cancellation.

A fun fact is that the leader of Overworks was Noriyoshi Oba, who was actually the "producer/プロデューサー" of the original Clockwork Knight games. He is listed in the credits as Noriyoshi Ohba (大場 規勝 in the Japanese version of CK2). Yosuke Okunari is also listed as a staff member of Overworks, and his name also appears in the credits for Clockwork Knight 1 and 2 under the "Special Thanks/マーケティング・スタッフ" portion as Yousuke Okunari (奥成 洋輔 in the Japanese version of CK2).

The following is a list of articles, etc, mentioning the game and it's existence:
http://archive.rpgamer.com/games/other/gamecube/knightknight/knightknight.html - Mentions the game
http://archive.rpgamer.com/news/Q2-2003/051303a.html - Article about the game
https://web.archive.org/web/20030622115056/http://www.the-magicbox.com:80/game051203.htm - Archive of page - Mentions the game
http://uk.ign.com/articles/2003/05/12/e3-2003-clockwork-night-sequel - Article about the game
http://uk.ign.com/games/knight-n-knight-142025 - IGN Game Page
http://www.ign.com/boards/threads/news-on-overworks-next-rpg-for-the-nintendo-gamecube.38925961/- forum talk about the game
http://www.the-nextlevel.com/tnl/threads/18831-Clockwork-Knight-RPG - forum talk about the game
https://segaxtreme.net/threads/sega-previews.6427/ - slight forum talk about the game
https://segaretro.org/Knight'n_Knight - Wiki about the game
https://nintendo-online.de/forum/showthread.php?5249-Clockwork-Knight-Sequel - German Language Nintendo forum posting about the game
https://web.archive.org/web/20030909132446/http://www.cube-europe.com:80/news.php?nid=4371  - Archive of page - Mentions the game
http://www.trademarkia.com/knightn-knight-76201256.html - Trademark registration for the game, with a potential logo
https://trademarks.justia.com/762/01/knight-n-knight-76201256.html - Second trademark site with a bit more info.
https://www.j-platpat.inpit.go.jp/c1800/TR/JP-2000-135092/06461060B15B37D305BF32DFE929C350A3231B4FD5E19D48CBEAB92B3E01BC5A/40/en - Japanese Trademark registration for the game, with a potential logo

I was the person to actually research and discover the Trademark page along with the potential logo myself back in 2012. It's funny how things can sit there for over a decade without anyone discovering it. But, that is the name of the game with unreleased video game research, I suppose. It helped me to confirm the games genuine existence outside of the very little "reporting" done on the game at the time of it's announcement, which was very important.

Speaking of the above trademark shown on trademarkia.com, the following information is avavailable:
Trademark registration was first filed on 29th January, 2001. 
It's serial number is 76201256 and it's registration number is 2814461.
The last applicant/owner of the Trademark was Kabushiki Kaisha Sega in Ohta-ku, Tokyo.
The correspondent for the trademark is David Ehrlich.
It's completed registration date was 17th February, 2004. 
It's filing expired on 24th September, 2010, due to the trademark not being used and notice of continued use not filed in time.

In addition, the Trademark listing on Justia.com gives a little more information on the registration process, including information of a Japanese trademark filing for the game on 15th December, 2000, with a application number of 2000-135092, and this was used to find the Japanese trademark listing on j-platpat.

Given the time of each filing (December 2000 and January 2001), it's possible that tis game actually started life on the Dreamcast before being moved over to the Gamecube after the Dreamcasts cancellation, before being outright cancelled itself. Given that the game was possibly somewhat worked on before the Trademark filing, and Overworks was not defunct until October 2003, it's possible that around 2.5-3 years of work went into this game before it was cancelled.

The above linked IGN article mentions the "Japanese press" talking of the game leading up to E3 2003 (on 12th May, 2003) and that it will be released in the "not too distant future", but after a thorough search on the subject via Japanese Google and using very certain search terms, I can find nothing of it.  Next step will be to contact IGN to see if they have a possible source for their article. It's popossible that this is lost after 13 years, but worth a try....
Although, based on my own independent research "the-magicbox.com" seems to have been the original source of the information, and everyone else just reported on it after the fact.

Another good step would be to look in gaming magazines of the era, possibly on the Japanese side, but also on the US side and POSSIBLY the EU side for any mention of the game at all.

That is everything currently known as far as I can tell. This text file is based on around 9 years of research into the title. Sadly, even after all this time not much is known. I can be contacted via spam at tongara dot co dot uk if you have any information I don't. Just put "Clockwork Knight Gamecube" in the subject~