You can start by turning on verbose mode and seeing which folder the
moonlib objects you're created are actually read from.
This is what I get:
tried /usr/lib/pd/extra/moonlib/mknob-help.pd and failed tried /home/ico/pd/mknob-help.pd and failed tried /usr/share/pd/mknob-help.pd and failed tried /usr/local/lib/pd/doc/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/postlude/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/cyclone/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/zexy/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/creb/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/cxc/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/iemlib/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/list-abs/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/mapping/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/markex/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/maxlib/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/memento/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/mjlib/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/motex/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/oscx/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/pddp/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/pdogg/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/pixeltango/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/pmpd/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/rradical/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/sigpack/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/smlib/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/toxy/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/unauthorized/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/pan/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/freeverb/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/hcs/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/jmmmp/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/ext13/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/ggee/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/flib/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/ekext/mknob-help.pd and failed tried /usr/lib/pd/doc/5.reference/flatspace/mknob-help.pd and failed tried /home/ico/pd-externals/mknob-help.pd and failed tried /usr/local/lib/pd-externals/mknob-help.pd and failed tried /usr/lib/pd/extra/mknob-help.pd and failed tried /usr/lib/pd/extra/moonlib/help-mknob.pd and failed tried /home/ico/pd/help-mknob.pd and failed tried /usr/share/pd/help-mknob.pd and failed tried /usr/local/lib/pd/doc/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/postlude/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/cyclone/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/zexy/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/creb/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/cxc/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/iemlib/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/list-abs/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/mapping/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/markex/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/maxlib/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/memento/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/mjlib/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/motex/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/oscx/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pddp/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pdogg/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pixeltango/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pmpd/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/rradical/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/sigpack/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/smlib/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/toxy/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/unauthorized/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pan/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/freeverb/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/hcs/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/jmmmp/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ext13/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ggee/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/flib/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ekext/help-mknob.pd and failed tried /usr/lib/pd/doc/5.reference/flatspace/help-mknob.pd and failed tried /home/ico/pd-externals/help-mknob.pd and failed tried /usr/local/lib/pd-externals/help-mknob.pd and failed tried /usr/lib/pd/extra/help-mknob.pd and failed tried /usr/lib/pd/extra/moonlib/mknob.pd and failed tried /home/ico/pd/mknob.pd and failed tried /usr/share/pd/mknob.pd and failed tried /usr/local/lib/pd/doc/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/postlude/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/cyclone/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/zexy/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/creb/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/cxc/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/iemlib/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/list-abs/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/mapping/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/markex/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/maxlib/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/memento/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/mjlib/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/motex/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/oscx/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pddp/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pdogg/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pixeltango/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pmpd/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/rradical/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/sigpack/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/smlib/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/toxy/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/unauthorized/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/pan/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/freeverb/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/hcs/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/jmmmp/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ext13/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ggee/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/flib/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/ekext/mknob.pd and failed tried /usr/lib/pd/doc/5.reference/flatspace/mknob.pd and failed tried /home/ico/pd-externals/mknob.pd and failed tried /usr/local/lib/pd-externals/mknob.pd and failed tried /usr/lib/pd/extra/mknob.pd and failed sorry, couldn't find help patch for "mknob.pd"
The help file is located in /usr/lib/pd/doc/5.reference/moonlib/ but pd never looks in there. It seems like something is missing inside the search path somewhere. But where?