Where is the Community Wiki? 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.