A node-red node runs as a headless piece of code in the server. It doesn't display anything on the screen. The imodel.js library you've linked to appears to be a library for displaying models on a webpage. Node-RED nodes don't run in the webpage - they run on the server.
There are modules such as node-red-dashboard that can be used to generate web-page dashboards served from node-red. It might be you want to create a custom node for node-red-dashboard that can be used to add an imodel.js viewer to a node-red-dashboard web page. But I am just guessing....
What do you want your custom node to actually do? Describe what functionality you want it to provide.
