We don't have "topic wikis". But we have 2 other things that might (or might not) fit your needs.
If you really have to or want to, you can convert each individual question and/or answer to a "community wiki" by going to
edit, selecting the
community wiki checkmark at the bottom-right, and the saving it.
But before you decide to go that way, please note that — when doing so — you won't gain or lose any reputation from votes, as a "community wiki" transforms things to a community thing.
Simpler stated: currently, upvotes result in a reputation gain for you. If you turn things into a community wiki, you practically give up ownership to that post and no one gains reputation from related upvotes.
Long story short: Think of a "community wiki" question and/or answer as a "selfless contribution to the community" which invites anyone to potentially edit and enhance the wiki-ed Q and/or A. As floorcat correctly mentioned: while surrendering reputation gains/losses your username will still be listed as the OP, so your (nick)name will still be visible to others.
Here's a practical example of what such a community wiki answer looks like.
Each question has one or more tags. If you click on them, you'll get to the related tag info page, where you can see the currently available information about a tag, and add or edit that information.
If no tag information exists yet, click the "help us create it" link:
If tag information already exists and you want to add to it, or enhace it, click the "Edit Tag Info" button:
Adding or enhancing a "Tag Info" is as simple as suggesting an edit to another Q or A.
Those two - "Community Wiki" and "Tag Info" - are basicly the two options that could fit your idea of a "topic wiki". If and what makes most sense to you, is for you to decide.