The JSON files to validate are controlled by this:
<property name="examples" value="/c/x3d-code/www.web3d.org/x3d/content/examples"/>
in the build.xml
There are also the options to include and exclude filename patterns.
Try this command, if you have Java and ant installed:
$ ant
there are additional targets in the build.xml to choose from.
Also, downloading and configuring location of X3DJSAIL.4.0.full.jar is essential.