Unfortunately you cannot get the port number since IISNode does not use ports and instead uses piped streams which is that random string you see for the port number. If you want to grab the actual HTTP port that the IIS website is running on, you would need to either parse the configuration file that stores this information or set it as an environment variable accessible by Node itself.
Is there a reason you need the port for your application? You shouldn't need the port to run the application as Node will treat that random string as a pipe instead of running server on a port.