You show a ‘get employee’. This allows you retrieve an employee from your application. What you describe to wannahave is a POST employee. That will allow you to insert your JSON and process it to become employee-objects in your app.
Mendix has created nice tools to setup the basics of an interface. Likely the training lets you do too much manually. Here is the quick route:
Now you are done with ‘publishing the employee-api’ :-)
To have a JSON without as little effort as possible:
Useful to have.