How/where to read the json file receive from notification? Unity SDK - Android Notification implementation.

[CaoDuThai]

As the moment I'm writing this issue, the guide for Unity SDK implementation is a bit outdated and under the process of updating.
The setup guide on this GitHub doesn't help us much with implementing other parts of Countly aside from the basic setup. In my specific case, I have trouble with implementing Notification.
At first my problem was: I sent the notification successfully but no notification was found on my application.

I double check on the user profile and it did receive multiple notification pushes that I have sent, all went through.

So, after I reread a bunch of out/new documents I found out that Countly ONLY sent data message and I have to handle to message on my app.
MY QUESTION IS: where do I find the json application received from notification?. How do I process it correctly? Is there any in-depth document about this? (I have searched with no luck). Is there a way for the notification to show automatically?
If I got anything wrong please feel free to point out because I'm a bit lost in this notification implementation right now.