here there is a manual
http://gershwin.ens.fr/vdaniel/Doc-L...ganizer-2.html
but the suggested option '-c' doesn't work with korganizer 3.1.3
i just run from command line:
korganizer <your_default_calendar>
this seems have written the default calendar in
~/.kde/share/apps/korganizer/docprefs.todolist.kconfig
my default calendar
and now when i start korganizer it open the default calendar.
hope it's clear and works