Yes, every GraphObject has a GraphObject.click event handler that you can define to open a browser window on whatever URL you like. For example, take a look at the click: defined in the Node template used in http://gojs.net/latest/samples/euler.html.
In that sample the click event handler is defined on the whole Node, but you could add a Shape or a Picture or a Panel containing Shapes or Pictures or TextBlocks to be at the top-right spot of the node. I suggest that you read http://gojs.net/latest/intro/panels.html and http://gojs.net/latest/intro/nodes.html.
If you are starting with the Node template from the FlowChart sample, I think you can just add your new “anchor” object directly to the Node panel, with
alignment: go.Spot.TopRight. That’s because the Node Panel is of type “Spot”.
But I still highly recommend reading the Introduction pages, http://gojs.net/latest/intro, because that covers all of the concepts you are likely to need in order to be effective programming GoJS.