Depending on exactly what type of CDN you are using, you may not need to do anything.
If you're using it for "storage" - in other words, you upload files to the CDN rather than your website - it will be difficult to handle with Q2A. You'll have to take all the static files in various places (the qa-content/ folder and your theme folder), put them on the CDN, then modify your theme code to link to those files instead.
If you're using a "proxy" type CDN - where your domain points to the CDN and the CDN calls through to your website - then Q2A will work fine. You don't need to do anything, the CDN will pick up which files are static and serve those from its cache.
I looked at the cdn77 site and they appear to do both so I don't know which you will be using, but it looks most likely to be the proxy type.