Yes, per device.
You then have 2 push tokens for this user, one for the iphone and one for the ipad, in your database both tokens must be assigned to this user. If you want a push notification for the user, you have to send the message to both tokens, because you can't know on which device the user is waiting for one of them. Instagram does the same thing for example, I have the app on my android phone and on my ipad, when someone writes to me I get the notification on both devices.
Or another approach would be to check which device was last active in the DB and then send to this device. But I would not recommend this.
I hope I didn't misunderstand your question.