The following URL works for me on Websphere 6.1 (Network Deployment configuration):
Code:
service:jmx:iiop://localhost:9100/jndi/JMXConnector
where 9100 is the ORB listener address on the node manager (accessible through the admin console via System Administration | Deployment Manager | Ports). Similarly, one could infer the URL for a stand-alone node by looking up the mentioned listener port number (admin console via Servers | <server_name> | Ports) for the application server.
Hope this helps,
Alex.