WorkerRemote r = // how to obtain reference? Should I use JNDI as ClientPOJO or @EJB annotation?
You can use @EJB injection since you are using it within another server side component (i.e. the @Stateful bean). However, that doesn't mean that you cannot use JNDI lookup. You can use JNDI lookup too, but @EJB injection is a convenient way of getting hold of the bean.