I haven't used JRun 4 so take my advice with a grain of salt...
1) JRun might not support you editing the deployed files directly. Have you tried to do a file search for a file you know the WAR contains, starting from the top-most directory of your JRun installation?
2) With auto-deployments, the context path is usually the same as the WAR file's name, i.e. copying foobar.war into the auto-deployment directory would result in the web application becoming available via
http://localhost:1234/foobar and so forth.