This article is for cPanel Accounts. Determine where your account is with this guide.
Once you have set up your addon domain and created an FTP user through your account's cPanel, enter the settings listed below to connect.
Host: ftp.yourdomain.com
Username: user@yourdomain.com
Password: password you created for the user
Directory: /
You can always use the main FTP account and publish to the addon domain's subfolder under public_html instead. In that case, you would set the directory to public_html/addondomain.com