My current understanding of APNS is that Apple will provide the different device token for each device. Based on device token, service provider will send the notification to device. So if we login with same account in two devices, then can we get single notification in two devices or only latest device? And if we send the notification to device,and device is in switch off mode.Then apns will return any error message and store that device token in feed back service list or wait for send the notification to device?
The precise question to your answer is that you can only get one push notification for the latest device that the user chose for login. Because of Apple's APNS architecture, it is not possible to receive the same device token on two different devices, regardless of both devices belong to the same user.
In order to send a notification to multiple devices, you'll have to adjust your data model in the backend such that one user can be associated with multiple device tokens. Then, when your event is triggered, you can send the notification to both devices (assumed of course the user is loggen in both).