Apparently there is something called "community wiki" on MO but I don't know how to find the questions,etc that are part of (or belong to) this wiki.
(I have a question/post in mind which would be suitable for a "community wiki" but I wanted to see some samples first.)
Being "community wiki" is a property of an individual post. Answers can be made community wiki by the person posting them, but since the move to MO 2.0, questions can be made community wiki only by the moderators. Therefore if you wish to make one of your questions community wiki, the way to proceed is flagging that question for moderator attention, and saying that you wish it to be made community wiki.
Regarding samples of community wiki posts, you can just browse MathOverflow and look for questions and answers which are marked "community wiki" in the lower right corner. If you are in doubt whether or not a particular question is suitable as a community wiki question on MathOverflow, just ask here on MathOverflow Meta.
To find all posts that are in Community Wiki mode (there is not really such a thing as "the Community Wiki" as explained by Stefan Kohl) you can use this Stack Exchange Data Explorer query. It will (it is hoped) list all questions in CW mode and all answers in CW mode that are not answering a CW question, sorted by creation date. In any case, it will give you a large selection of CW posts.
However, please, be aware that not few of the questions you can find on this list are closed and more would in all likelihood be closed when asked now.
