The following command entered in Terminal will enable the Debug menu in iCal (Lion):
defaults write com.apple.iCal IncludeDebugMenu YES
I would like to accomplish the same thing in Calendar (Mountain Lion).
A menu is most desirable, so this is not a proper answer, but here goes …
It's possible to do at least some of the things that were possible with the menu.
Some of the things that were in the Top Sekret submenu of the Debug menu in iCal …
5 or 7 days: Use the General pane of Calendar preferences.
14, 21 or 28 days:
defaults write com.apple.iCal "n days of week" 14 defaults write com.apple.iCal "n days of week" 21 defaults write com.apple.iCal "n days of week" 28
The change will be effective when you next switch to week view.
⌘+L is not effective. I'll investigate …
I found this:
defaults write com.apple.iCal CalUIDebugDefaultDaysInWeekView <# OF DAYS>
I had Debug enabled in Lion, showing 2 weeks in iCal. Upgraded to Mountain Lion and could't get it back to one week view until I found Mountain Tweaks.
Under the Lion tab (not Mountain Lion) I clicked to disable iCal Debug and it worked. It's a free download but I donated to the developer.
Unfortunately this option seams to be gone forever, scan thought iCal's files from 10.7 gives two options that contain 'InsertDebugMenu'. However same scan on calendar's file from 10.8 doesn't show any of them, as a matter of fact this version is lacking more then few 'debug' commands that until this release were only hidden but still accessible. My worst nightmare is slowly coming true, OS X soon will be just as closed as iOS is already :/
In case someone with more time, skills or luck will read it, you can try find something on your own with help of this post.
The debug menu was great because it allowed you to display the CalDAV queue of events. Calendar under Mountain Lion is not fully compatible with MS Exchange and has a tendency to hang in "Updating…".
Worse, it gets into a mode where it cannot update the Exchange calendar at all and you must choose from a very DOS style "abort, retry, fail" sort of dialog. Once in that mode, your calendar will not talk to Exchange until you delete the Calendar's cache file. This Cache file apparently becomes corrupt and causes a discord between Calendar and Exchange.
Deleting the cache file is no issue as Calendar just rebuilds it when Calendar is launched again. Don't forget to Quit Calendar before deleting the cache file, then launch Calendar to have it automatically rebuild. No data is lost.
The Calendar cache file is located here:
This happens once or twice a day to me so I keep that folder in my dock and I keep an alias to the Calendar app in that folder so I can launch calendar, quit calendar, delete the cache file, launch calendar. Welcome to Mac OS X… (sigh)
OnyX is a great little program, and has an option to enable the debug menu for calendar.
Alternitively, you could try
com.apple.Calendar IncludeDebugMenu YES in Terminal, although I’m not 100% sure it will work.
This isn't the answer you want, but I think the Debug option has really been disabled. However, I have filed a RADR to reinstate it in an upcoming dot increment (hopefully .2 or .3).