How can I distable coub.com weekly notifications
Assuming the notification is really coming from the coub.com website, you would disable that in Safari preferences, not System Preferences. 

Go to the Safari Preferences > Websites tab, select Notifications on the left, and you'll see a list of all the websites that have asked you for permission to send notifications. From there, you can change the notification preference for coub.com to "Deny".