Quick start plugin has an example on how to add a new api route https://github.com/NodeBB/nodebb-plugin-quickstart/blob/master/library.js#L40-L76.
The hooks that are fired client side are for client side code in plugins. If you want to pass data from the client to the server you have two options.
Create an api route like in quick start plugin
Create a new socket event listener on the server side and use socket.emit() client side. Example here
