Although the DWQA Questions and Answers plugin for WordPress has been updated to work with Multisite, it probably won’t work as expected. At the time of this writing, the problem appears to be new user creation and the multisite default functionality. In order to accept the DWQA default method of answering questions, which is that only registered users can post answers to questions asked by anonymous users, you have to allow them to register. First, on my Multisite subsite I had no option to allow user registration. Even after enabling it at my main blog as network administrator it was not available under the subsite options.
Other users have reported that once you are able to allow registration on a subsite, that clicking the link will redirect the user to the network main site and allow them to register there, which is probably not the desired action for a DW Questions and Answers site. It also allows that user to be login to all other sites on the network.
What would be desired here is either a separate login that is not tied to the wordpress registered users login, or the use of social apis so users could use an existing social account to login for posting and answering questions.