By reading this article you are already glancing at the heart of eXo Kernel.
Even you will read in this article to open the directory "exo-tomcat", you may have installed eXo Portal on any application server, just replace "exo-tomcat" by your folder name.
If you only installed the all-in-one package for the eXo Portal, the folder paths are a slightly different. You have to replace exo-tomcat by exo-eXoPortal-2.5.1-tomcat (obviously depending on your version). Furthermore the webapps are delivered as war files.
You certainly already discovered eXo's fisheye URL (eXo is open source!) - https://anonsvn.jboss.org/repos/exo-jcr/ - which allows you to surf in the source code of all classes, if you wish to do so.