In general usage (and hopefully correct usage) a "notifier" is someone who notifies.
What is the word for the person who is notified?
For example: "Instruct each [X] to respond to the notification within 3 days."
Learn English – The word for “Those who are notified”
grammarsingle-word-requests
Best Answer
While I expect that you're looking for something like notifiee, I'm not aware of any such word that would have that exact meaning. That being said, there are several good options that could work:
In the general case, (though these may overuse the notify root for your taste):
If the notification is a written message that they received.
If the notification is some sort of pop-up in a program