This depends on whether your domain is installed on a server with Confixx or Plesk Control Panel.
With the Confixx Control Panel, all your domains share a directory.
It is the html folder. The full path is /var/www/webXXX/html where webXXX is replaced with your web user (eg /var/www/web123/html).
If you want to display different content for two domains, you need different subfolders in this folder. After you have created these subfolders, you can use the Confixx Control Panel under “Settings> Domains” specify in which subfolder the website is located.
On a Plesk server, each domain has its own start directory. It is the /httpdocs directory and the full path is /var/www/vhosts/yourdomain.eu/httpdocs