I don't think we can say that "someone owns Ask Ubuntu".
The system and the engine that runs this site is provided and maintained by Stack Exchange whereas all the content and contribution of members is licensed under cc-wiki.
This site has come into existence by a democratic process and the strength of every Stack Exchange site is its users and members. I don't think we can say that the site is owned by Stack Exchange. But they are the maintainers of the engine and act as trustees to ensure that the site is run properly. Stack Exchange derives its revenues through this model, so well-run sites definitely help them creating goodwill.
Whereas, Ask Ubuntu is also regarded as an Official Support channel for all things Ubuntu. And Ubuntu involves the whole community around Ubuntu. So, once again this is not owned by someone.
Basically, I think each and every site in Stack Exchange network is not owned by anyone. Stack Exchange is at the core of every site, but they are the maintainers of the engine - I wouldn't regard them as the owners of the site (because of the fact that the strength of the SE model is its members).
What I consider is that the community owns Ask Ubuntu (and every other SE site).
PS: The above is just my opinion without going into technicalities and the legal stuff.