Your website file must be uploaded into the public_html directory, which is, in general, the document root folder for your primary domain name associated to the hosting service.
If you are hosting additional domains, which are added as Addon domains or sub-domains in cPanel, they have their own document root folder and should be found in account’s home directory (above public_html).
You can easily locate the document root for an addon domain from cPanel > Domains > Addon Domains and look at Modify Addon Domain section.
As for any sub-domains, you can easily locate the document root from cPanel > Domains > Subdomains > Modify a Subdomain section.