A full server path is the path your system uses to define where your own files are located on the server (as opposed to files belonging to other users).
You can determine the path while you are logged in via FTP (some programs will tell you this) or while using a File Manager tool in your Control or Administrative Panel (if your host provides one for you).
You can create a pathinfo.php file. Open a plain text editor, and paste in the following:
<?php echo $_SERVER["SCRIPT_FILENAME"]; ?>
Save the text file as pathinfo.php. Upload the file to your server.
Now, type the URL to the file you just uploaded into your browser to view the full server path to that file.
If none of these solutions work, you may need to ask your host for the full server path for your system and account.