K is our screenshot Key as Blade says - from the FAQ section 24. ..
"By default they will be in your Documents in Windows, once there look in the
OBDWW2 Wings Over The Reich folder.
So for Windows 7 and Windows 8, and 10 users:
browse to C:\Users\Your Logon Name\Documents\OBDWW2 Wings Over The Reich
If you find no screenshots, or K is not working, make sure you don’t have mods installed such as SweetFX as it may override any game screenshots and stop K key from working at all. Sweetfx can use PrntScrn key to take screenshots, but it saves its own screenshots to the sim’s main folder.
For example C:\OBDSoftware\WOTR\ OBDWW2 Wings Over The Reich.
"