Hi Jerome,
a good place to start at might be the Solace JMS API-Documentation here:
JMS API
First of all you must make sure that the JNDI Provider can connect to Solace properly by displaying list of all objects which can be looked up in this JNDI Context.
After that you can try to configure the JMS Provider Alias with the ConnectionFactories used to look up the queues and/or topics to connect to.
You can also refer to the webMethods Messaging Guide.
Regards,
Holger