Many of the GoXam samples were ported to GoJS when we first implemented GoJS. However more recently we have made changes in order to improve the styling of the samples, something that we explicitly avoided in GoXam.
The biggest change involves moving from a desktop application to a web application. That does not involve GoXam or GoJS, so we cannot help you there.
I assume you are very familiar with WPF, is that correct? So if you are not already fluent in HTML/CSS/JavaScript, you’ll need to learn those first.
I suggest that you learn GoJS by reading Get Started with GoJS and then all of the Introduction pages that apply to the kind of app that you are porting: GoJS Introduction -- Northwoods Software. As you learn GoJS you will see how the overall design is similar to GoXam and WPF, although the details are different.