Where do you have samples GUI and source code for the GraphObject click event?
How would one customize the “GoJS Building Parts with GraphObjects” example to click and object node and assert a desired comment?
All of the samples are at http://gojs.net/latest/samples.
Better yet, get the whole web site from http://gojs.net/latest/doc/download.html – there’s a link to a site.zip file. Then you can search all of the samples and introduction for whatever feature(s) that you like.
To answer your particular question, perhaps the http://gojs.net/latest/samples/arrowheads.html sample demonstrates what you want.
But you really ought to read http://gojs.net/latest/intro/events.html, which talks about different kinds of events, including the GraphObject.click handler.