@baris error is gone / fixed. Thank you!
Now that I re-read what you originally asked, I'm curious if you actually need "Sockets" (as in SocketIO, which is server-initiated TCP/IP connection to a browser) or if APIs on both the hosted NodeBB server and the localhost server would do this better.
Either way, if you choose to go the NodeBB plugin route, you will need to know which Hooks are available. A "hook" is an event that your plugin subscribes to. When that event happens in the core NodeBB server, it will call the function in your plugin which subscribes to the event.