When a message contains a mention for someone, a other message is created by Tat Engine in topic /Private/username/Notifications, where username is the user mentioned.
Example :
see result in screenshot below for these two messages in topic /Private/yesnault/Notifications
In plugin.tpl.json file, add this line :
"tatwebui-plugin-notificationsview": "git+https://github.com/ovh/tatwebui-plugin-notificationsview.git"