You can find an example by going to the main Eikon menu accessible by clicking on the Eikon logo on the leftmost of Eikon toolbar, then selecting Developer tab and clicking on JET.js API demo. Then in the window that pops up navigate to News Plugin. Here you can find an example of creating a subscription for news headlines.
Please note that some of the content in JET.js API demo is outdated. I very strongly recommend you to reach out to the developer advocacy contact assigned to your project from Thomson Reuters side, who will be happy to guide you through the architecture of App Studio and through the API you need to use.