It looks like the Community Wiki checkbox is no longer appearing on the ask/edit question page, making it difficult to mark questions Community Wiki.
Where is it, and how is one supposed to mark a question as CW now?
see:
We removed that option globally from all questions.
If it really needs to be wiki, flag it for moderator attention, it was causing confusion and pain.
We have provided some additional guidance at the blog:
https://blog.stackoverflow.com/2011/08/the-future-of-community-wiki/
TL;DR version
Most of the time, you should be asking yourself “How can I improve this post so that community wiki isn’t needed?” Community wiki is like a cheese knife: it is a specialized tool to be used sparingly, and only in very specific circumstances.