You need a notification view hook to specify template for viewing your notification type item in notification list.

A working example can be found on https://www.opensource-socialnetwork.org/component/view/5526/notification-sample

<?php
function my_component_init(){
		//example for type `notification:message:tomyself`
	    ossn_add_hook('notification:view', 'notification:message:tomyself', 'notification_sample_myself_view');

}
function notification_sample_myself_view($hook, $type, $return, $params){
	$notif   = $params;
	$user    = ossn_user_by_guid($notif->poster_guid);
	$url     = ossn_site_url("u/".$user->username);
	$iconURL = $user->iconURL()->small;
	return ossn_plugin_view('notifications/template/view', array(
			'iconURL'   => $iconURL,
			'guid'      => $notif->guid,
			'type'      => 'notification:message:tomyself',
			'viewed'    => $notif->viewed,
			'url'       => $url,
			'icon_type' => 'alert',
			'fullname'  => $user->fullname,
	));
}
ossn_register_callback('ossn', 'init', 'my_component_init');