By default the MacOS X Open Directory debugging log file is disabled. You can temporarily reenable it by running the following command in the Terminal app:
sudo killall -USR1 DirectoryService
After you reboot, debugging will be disabled again. If you want to enable Open Directory debugging so that it stays enabled across reboots, run the following command in the Terminal app:
touch /Library/Preferences/DirectoryService/.DSLogAtStart
To disable debugging again just delete that file:
sudo rm /Library/Preferences/DirectoryService/.DSLogAtStart
The debugging log file is located at:
/Library/Logs/DirectoryService/DirectoryService.debug.log