Yes, when a node is selected, or just when the user clicks it, you can show some HTML with details about the node. This could allow people to edit some of those details too.
Each such display of details and way that you let users edit them is very application-specific.
Furthermore, as an expediency to get you started, GoJS offers a Data Inspector as an extension. It shows a list of properties and lets the user edit their values. Examples:
But in the long run most apps want to implement their own custom HTML for showing and editing each of their types of nodes. And maybe links too.