It depends on the product, but usually in menu > about > subscription or license.
Where do I find the AVG License Number?
Hello Kamal,
I see that you have purchased the license for AVG Internet Security (1 computer).
If you have installed the latest 2017 version of it then you can open the dashboard and click on "Menu–>About–>Subscription"
The license number will be hidden with the "X" symbol due to security reasons.
You can check the license number by logging into AVG my account using this link: https://myaccount.avg.com/my-account-login .
If you still couldn't find the license number do let us know.