/usr/share/doc/libjs-mathjax-doc/html/_static/jquery.js is in libjs-mathjax-doc 2.7+20171212-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libjs-mathjax-doc/html/_static/../../../../javascript/sphinxdoc/1.0/jquery.js