What you probably refer to is service lookup. From the spec: "The lookup service provides a central registry of services available within the djinn. This lookup service is a primary means for programs to find services within the djinn..."
As for disccovery: "Entities that wish to start participating in a distributed system of JiniTM technology-enabled services and/or devices, known as a djinn, must first obtain references to one or more Jini lookup services. The protocols that govern the acquisition of these references are known as the discovery protocols."
I think you have to know your types you want to use. What are you going to do with an interface you know no nothing about?
When you know the interface and what it is good for, you build your program relying on it. What you get in Jini by a service lookup is an implementation of that service interface.
I am aware my answer is sketchy. I would like to direct you to the place where Jini continues its existence: river.apache.org. Jini is live and well! Use the specifications, examples and of course the mailing lists to get an exhaustive answer.
Cheers.