Why I cannot see application menus on the 2nd extension screen of Mac?
This happens to me when my second screen is a TV. Some screens chop off the edges of the screen.

Here are three things I'd try:

1 Mirroring


  
  Go to System Preferences » Displays
  Select "Arrangement"
  Click "Mirror displays"
  



Image via http://support.apple.com/kb/ht5019

This makes both monitors display the same screen, forcing them to be the same aspect ratio. If the aspect ratio is different, there will be blank space around the image.

2 Change screen resolution.


  Go to System Preferences » Displays.
  Try changing the resolution for your second screen.


The system will ask you to confirm if the settings work, so you don't have to worry about accidentally messing things up. Go nuts.


Image via this StackOverflow question, since I don't have a second display connected right now.

3 Change the settings on the monitor itself.

If the menu bar is still missing, try using the monitor's menu to change the crop settings.

This is isn't as likely with modern monitors, but it's a possibility (especially if you're using a CRT monitor or TV)

More notes

If you see a menu bar on top but it's blank, the options should appear once you click on that screen.