The print PDF button gives an identical file for the same version of a current page. The next step would be to test if an offline wiki with the PDF plugin gives a file with the same hash for the same page. That would be as close to reproducible as we can get.
So for a given version of the Whonix manual a user would download a snapshot of the wiki tarball (when it was used to generate the official PDF) and setup an offline mediaiwiki and generate a PDF and see if the file matches with the (signed) official one provided.
At the moment Whonix and TAILS are at the same level on this. They just use ikiwiki instead and commits are made via git pull requests instead of the easier mediawiki editing but they don't have an easy to read file thats reproducible for offline use.
If you think this is too much work forget it.