So the general gist:
1) Notifications would be a polymorphic association in that comments can have many notifications, users can have many notifications, a ‘following’ can have many notifications etc.
2) You can have Model Observers, where you can “observe” certain events, such as when a new comment is created. This is would be your triggers.
In terms of routing, you really don’t need to do anything out of the norm. The only routing you may have is a domain.com/notifications where it shows all the notifications.
Notification table might look like:
sender_id: integer, receiver_id: integer, notifiable_id: integer, notifiable_type: string