WordPress QnA plugins enable users to post questions and answers (Q&A) in a Stackoverflow style. After the installation of this plugin, your WordPress site will have a full-featured question & answer section. Here is the list of Best WordPress QnA plugins.
1. DW Question & Answer
DW Question and Answer is a WordPress plugin which builds a complete Question & Answer system for your WordPress site, like Quora or StackOverflow. The plugin supports multi-languages, shortcodes, reCAPTCHA, email notification system and so on.
2. CM Answers
CM Answers is a plugin for WordPress that enables users to post questions and answers (Q&A) in a Stackoverflow style. Plugin also includes social media registration using Facebook, LinkedIn or Google+, Twitter & Microsoft Live authentication. The CM Answers discussion forum plugin has many other unique features which allow administrators to customize it according to his or her needs.
3. AnsPress – QnA
Easily add a question and answer section like stackoverflow.com or quora.com in your WordPress. AnsPress is a complete question and answer system for WordPress. The Plugin is made with developers in mind, highly customizable. AnsPress provide an easy to use override system for the theme.
Easily add a Question & Answer community to your existing site or create a new stand-alone community. WP-Answers was the first comprehensive Question & Answer system for WordPress and remains the best. Kick start your community by pulling content from Stack Exchange API and make your site look busy from the start.
5. Sabai Discuss
Sabai Discuss is an ideal tool not only for building a community driven question-and-answer website but also for building a discussion forum, a knowledge base, or even a helpdesk portal for WordPress. The plugin features the ability for users to ask and answer questions similar to Stack Overflow or Yahoo Answers.
I hope this list would be helpful. Do you use Question and Answer Plugin on your website?