When building a skill that communicates with an outside service (like Napster or Spotify) the core of your skill will likely use APIs from those services to fetch and manage data on the side of the outside service.
A simple example of using APIs in the Jibo SDK can be seen in this early post that discusses using Philips APIs to control a lightbulb with an SDK built skill. You can take a look at what APIs Spotify and Napster have available here and here.
Another example of creating an Jibo skill that reaches outside services can be seen in this post that discusses connecting a skill in the SDK with IFTTT.
I would use those skills (along with our starting tutorials) as a good place to begin with a skill like the one you described.
For a more broad overview of tips and tricks for developing a skill you might find our live stream with our Executive Producer, Andrew Rapo, interesting.
I hope those resources are helpful for getting started!