When a platform event is fired, it is consumed from whichever client is subscribed to its specific channel.
If a single event is fired and consumed by 5 consumers, it will count 5 against the Daily Limit, which is 25k.
Salesforce provides who is subscribed to a Platform event since this subscription is performed with a Process Builder or an Apex Trigger. There is no way, as far as I know, to know/understang who from outside Salesforce, for example CometD clients, is subscribed.
Does anyone know if this is by any chance possible?