All customizable properties in DocBook-XSL (parameters, attribute-sets, processing instructions) are already "dumped" in the documentation: http://docbook.sourceforge.net/release/xsl/current/doc/.
The font properties for XSL-FO that you mention are XSLT parameters:
- http://docbook.sourceforge.net/release/xsl/current/doc/fo/body.font.family.html
- http://docbook.sourceforge.net/release/xsl/current/doc/fo/title.font.family.html
If you haven't customized these parameters, they have the default values shown in the documentation.
See also these sections from "DocBook XSL: The Complete Guide":