Hi there @mansi.srivastava ,
At first, I was confused as well.
This endpoint GET https://{YOUR_DOMAIN}/API/v2/name-templates will return only templates that have been already modified.
You should be able to find most of the emails code in your Auth0 tenant → Branding → email templates. One exception is the passwordless email Passwordless Email OTP, which is available under Connections → Passwordles → Email. Ref.
Please let me know if you encounter any roadblocks while modifying your templates.
Another thing to note is that when you test your new templates, you must first set your Custom email provider. But as all of them are just HTML files, you can test the appearance in your browser as well 