It is clear how a question or answer can become community wiki, but I can't find any documentation for how to find these questions to participate in answering them. I came across a few questions in a search that had a community-wiki tag (probably here), but no such tag is listed in the tags list and a search on that tag comes up empty. I also can't find any type of link. Is this like write-only memory?
The search box supports a variety of extra search terms such as
wiki:yes ( or ":no") and
This search will show you all the questions which are community wiki: https://superuser.com/search?tab=newest&q=wiki%3ayes%20is%3aquestion
On the search page on the right hand side near the top is an "Advanced search tips" link which will show you the extra tools you have.