Coming from this comment: is it possible to create a community wiki during the private beta?
Yes, it is possible to create a community wiki answer. But there is rarely any case for it. Community wiki was primarily useful in the old days when there was a minimum reputation requirement to edit posts. Now, anyone can suggest an edit (which will be reviewed if the editor doesn't have enough reputation), so community wiki has lost most of its use. FAQ-type posts have also been replaced by tag wikis to a large extent. You may want to use it on an answer to encourage others to contribute to it actively, but that's very rare.
It is not possible to create a community wiki question. The possibility used to exist, but was removed because there was no good use for it. On Stack Overflow, it used to be a way to tolerate bad questions, but this is no longer done.
Community wiki answers are still used on meta sites, which don't have suggested edits, for things like FAQs.