2
Check out this link
http://dev.xoops.org/modules/phpwiki/index.php/Commentsystem
It should not be too hard to add comments. It may be easier to get the first two steps by looking at the url of the page you want to add comments.
You will see the page name and the id number within the url.
I plan on trying this in the next few days, it appears to be straight-forward.