JACK® documentation is provided as part of the JACK Documentation package. This package is separate from JACK itself. Once installed, the documents (in PDF and HTML format) are in the doc subdirectory. You can access the JACK documentation from the Help menu of the JDE.
There should also be a link in the automatically installed menu or shortcuts. If not, point your browser at the file doc/jackdocs.html in the place where you installed JACK and it will guide you to all the available documentation.