Kunena no notification for one user
If in your forum the default setting for getting notifications of posts is active, then you can disable that for one user. When that user makes a post, the checkbox to get notifications, which would else be selected, can be set to un-selected with this code.
version: Kunena 1.5.11
file: components/com_kunena/template/default/fb_write.html.php (where default is the template you are using, else template_ex/ or template_gray/ etc.)
where 99 is the id of the user which is not to recieve notifications.