Get OS X Notification Center State From the Command Line On OS X 10.8, users can disable Notification Center for a single day. Is there a way to check if it is enabled from the command line?.
You actually can find out if the Do Not Disturb is currently enabled or disabled.  Notification Center drops a plist in the following location that you can read the value of.
Run the following to find the plist file:

ls ~/Library/Preferences/ByHost/com.apple.notificationcenterui.*.plist


Now, you can read the value from the plist you just found by using:

defaults read ~/Library/Preferences/ByHost/com.apple.notificationcenterui.8D3EA20D-8D7F-52E2-9F99-BC17A13A3F0E.plist


NOTE: your actual filename may be different than what I have listed above.

You will see a key called "doNotDisturb" and it will either have a value of 1 or 0 (enabled or disabled)

You can also change it's status by doing:

defaults write ~/Library/Preferences/ByHost/com.apple.notificationcenterui.8D3EA20D-8D7F-52E2-9F99-BC17A13A3F0E.plist doNotDisturb 1


or:

defaults write ~/Library/Preferences/ByHost/com.apple.notificationcenterui.8D3EA20D-8D7F-52E2-9F99-BC17A13A3F0E.plist doNotDisturb 0


To make the change take effect, you'll need to restart Notification Center by typing:

killall NotificationCenter


I've actually written a very simple Automator script so now I can enable/disable the Do Not Disturb for Notification Center with a keyboard shortcut.  Very handy. :)