1. You can check the xf_user_push_subscription
table, this will have an entry for every device that is registered for push notifications (along with the user_id
)
2. If it is possible, it'd probably be done through Communication -> Contact users -> Alert users
, but I'm not sure if this is hooked up with the push notification. You can test it by sending one just to yourself though
3. I don't think this is tracked anywhere, at least not that I've seen