Enabling Assetto Corsa for your DK2 is not that easy. Here is what worked for me.
In documents/Assetto/Cfg open video.ini file and change the top section as follows:
Set DK2 into extended mode in the Oculus Config tool.
In the Screen Resolution window set your Oculus to primary display:
Launch the game into the menu screen but not the game yet.
Hold shift+start (Windows-Key) & then press right or left arrow (depends on if your Oculus is left or right) until the menu appears on your main monitor .
When you launch the game it will be on DK2.
Ctrl + space to recenter your view. Enjoy!