I know how to create a dialog in Sketchup ,by I don’t know how to create a panle on the right.
the only possibility is to create Instructor panel content specific to your extension…
you cannot create a persistent panel for an extension…
not persistent panel just a temporary panel ,which show up when clicking the extension button
This is not supported but has been requested for a long time. Feel free to like and comment on the official API issue tracker issue: https://github.com/SketchUp/api-issue-tracker/issues/384