Do we have calendar push notification in C also?
The Google Calendar API supports push notifcations you can use the Google Calendar api in any language that supports http post or http get.
How to get notification channel id?
From the documentation documentation
Register the domain of your receiving URL.
For example, if you plan to use https://example.com/notifications as your receiving URL, you need to register https://example.com.
Set up your receiving URL, or "Webhook" callback receiver.
This is an HTTPS server that handles the API notification messages that are triggered when a resource changes.
Set up a notification channel for each resource endpoint you want to watch.
A channel specifies routing information for notification messages. As part of the channel setup, you identify the specific URL where you want to receive notifications. Whenever a channel's resource changes, the Google Calendar API sends a notification message as a POST request to that URL.
Directly from the documentation
What does domain means in this context? Domain will be gmail.com always.
Domain will always be your domain you don't have control of gmail.com so cant get satisfaction to that.
Can you share a sample which can show working push notification of calendar?
The documentation page contains information on how to use push notifications. this is not in C. you will need to code your own implementation of this.