Every domain and subdomain hosted on your hosting account has a root or public folder. This is the folder where you have to upload the website or application files.
Every hosting account has a main domain and the root folder on the main domain is always the public_html directory.
You may host additional domains with full websites of you hosting account, in order the know their public folder access the Hosting Panel and click on Hosted domains icon.
You will see a listing of domains with their respective public folder.
Each subdomains do also have a specific public folder. Access the Hosting Panel and click on Subdomains icon.