If you browse to the '..\Divinity II - Developers Cut\bin' install folder in Windows Explorer, right click on the Divinity2.exe file and select Properties, then switch to the Compatibility tab and check off 'Disable desktop composition', you will be able to use the Print Screen button to take screenshots. Do the same for Divinity2-debug.exe (also, if you open the Developer Mode cheat window (F11) and hit the 'debug keys' button in the bottom right column to toggle them on, the H or ctrl-H hotkeys will toggle the UI on and off, which may be handy for taking screenshots).
Running the game in a window could also help, but I havn't tried that with Divinity 2 (there is a
configuration file edit to run the game in a window, or you can use the
Windows Borderless Gaming app).
There are also screenshot programs designed for use with games, but I haven't tied any to get around this black screen problem with newer games / DirectX (fraps is primarily used for capturing video, but can also be used for screenshots).
