The 'npm help' command does not work properly, because it cannot find the installed man pages. The help subcommand, implemented in help.js, looks for man pages in ../man (relative to its location). This means /usr/lib/node_modules/npm/lib/../man. This file does not exist. The problem can be solved by putting a symlink there: libdir=/usr/lib cd $libdir/node_modules/npm && ln -s ../../../share/man The approach can be used as a quick fix. While this works fine, it also has a downside: 'npm help <topic>' will search though all files with basename like <topic> there, starting with npm-<topic> and then <topic>, it seems (I have not verified this in the code, though). This means that npm help mv will show the man page mv(1), even though it does not belong to npm or nodejs. The problem can be remedied by creating $libdir/node_modules/npm/man/manX directories, with many symlinks to the /usr/share/man/manX/<manpage> files. This seems to be the technically best solution, in my opinion. (The basic problem has also been mentioned in bug 425520 comment 3.)
Closing due to inactivity, please reopen with updated information if this is still a problem.