[vbresults]

1. Go to AdminCP > Plugins & Products > Add New Plugin
   
2. Set the fields as shown (if you don't see something listed, you can leave the default value):
   
   Hook Location: global_bootstrap_init_start
   Title: Forum Path
   Plugin PHP Code:
   
   PHP Code:

   if ($_REQUEST['do'] == 'path') { var_dump(dirname(__FILE__)); exit; } 

   Plugin is Active: Yes
   
3. Save the plugin.
   
4. Visit to your forum's index and add

   ?do=path

   to the url, and press enter. The result should be your forum path.
   
5. Delete the plugin you just made.