There are no libraries or plugins that i know of. Possibly a lot of Q&A programs have API's. You could use those to integrate a Q&A in your app.
There is this example such an app made in CI.
http://kroud.co/
Maybe the owner can help you?
That being said.
A better place to start is to outline for yourself what you want from your Q&A. In terms of features, goals, etc..
Right now that is not very clear to me.
You can make a lot of things in CI and there won't be a library or tutorial for each of those things!