I have MacBook Pro Retina running Windows 8.1. I do not have a PrtScr key. Also, shift+fn+f11 key combination doesn't work. What is the shortcut to take screenshots?
⇧ shift+fn+F11 is the correct keyboard shortcut to emulate a Print Screen in Windows, however this shortcut requires the Boot Camp drivers to be installed and be running in Windows. Make sure you have the drivers installed correctly and check whether the keyboard is configured to require fn in Boot Camp Control Panel.
The FN+Option+Shift+F11 (and also FN+Shift+F11) will only work if you have the setting on Boot Camp Control Panel tuned off (unmark the checkbox): Keyboard tab > "Use all F1, F2, etc. keys as standard function keys..."
FN+Shift+F11 = Captures the full screen
FN+Option+Shift+F11 = Captures the current active window