Right now, the link to "post a comment" to a wiki page is only shown to registered. Is that how this site should be configured, Alain?
There is no link to "discuss" (to be sent directly to this forum, where anonymous can post through anti-bot code).
If you want to grant permission to anonymous users to post comments on wiki pages, then you need to grant that perm. to "anonymous" group through "Admin > Groups > key ", select to filter for forum permissions, and add whatever permissions are needed to do so (ask if in doubt)