I am running a cloud scheduler with firebase functions and would like to send the specific user a notification when something in the cloud using node js has completed, I researched about cloud messaging but it send it to everyone, I don't want that, how can I achieve what I'm looking for
You can send notifications to a specific app instance by targeting the FCM device registration tokens.
https://firebase.google.com/docs/cloud-messaging/send-message#send-messages-to-specific-devices