Implementation of Observer over the Web

I had a Job interview the other day and they asked me interesting question

In a abstract way describe a generic way to notify manager or certain member of an Event of sum form that happened in way of the member in a network 

My answer was to do it with an event that any one who want to be notified should subscribe it.

My question is this: how can it be done over a network of some sort.

Regards 
Matan