You can get EPP code at HostGator by contacting them or following these steps:
Login to your HostGator customer portal.
Go to the Domains menu.
Select the relevant domain name.
Navigate to the icons on the left and click on the Domain Locking option.
On the newly opened page, toggle the button to the Locking OFF position to unlock the domain and click Save Domain Locking to save the changes.
Click the Request Your EPP Key button to obtain your Auth code.
Completing these actions you will receive an email with your domain authorization code in just a few minutes. Now you will be able to transfer your domain to Hostinger :)
NOTE: You can also check this article for more information about the EPP code.