[easy is in the eye of the beholder]
[when you say highlight, I assume you will accept changing line or fill color]
I know of no “built-in” way to do what you ask, however:
- CSS seems to support changing colors based on “hover” (not click) (you would use the Graphviz “class” attribute)
- you can post-process the svg output to add “onclick” attributes to the svg as well as associated javascript. (Easy if you’ve written javascript before, otherwise maybe not)
Here is a link to a similar question with useful answers: Can I make a Digraph node interactive