Question: Is there any difference between how GET/POST works while in HTTP or HTTPS protocols?
What is visible in HTTPS GET/POST packet when you try to sniff the data? host IP? domain name? full GET request? 
What information TLS hides after successful handshake?

I can't seem to close this knowledge gap by looking in the internet, there's just no such question asked.

Please advice, make it reference for the internet.

Answer: 
1. URL begins with “http://" in case of HTTP while the URL begins with “https://” in case of HTTPS.
2. HTTP is unsecured while HTTPS is secured.
3. HTTP uses port 80 for communication while HTTPS uses port 443 for communication.
4. HTTP operates at Application Layer while HTTPS operates at Transport Layer.
5. No encryption is there in HTTP while HTTPS uses encryption.
6. No certificates required in HTTP while certificates required in HTTPS.
I presume your confusion is not on http & https, but it is more on GET & POST http methods.

To make it clear, data is not encrypted neither in GET nor in POST. Go through this [link](http://www.w3schools.com/tags/ref_httpmethods.asp) which summarizes the differences between GET & POST.

As Sanjeev and Imran mentioned, data is encrypted in https whereas it is not in http protocol.