After installing json-server by
pip install json_server
You can run
json_server <path-to-JSON-file> <port:optional>
The port argument defaults to 5000 
This shall output:
 * Serving Flask app 'json_server.main' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 816-527-262
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
Which is similar to what a standard Flask app logs.
Now that you have run the command, http://127.0.0.1:<port>/ shall respond with your JSON.