Root Moto G 2nd Gen 6.0 Marshmallow Edition

Steps:

Download and install latest driver of Motorola Link: Download
Make sure your boot loader is unlocked if here is the guide
Download the file: SuperSu Auto Flash
Boot your phone into boot loader by pressing power button and volume down button simultaneously for a time
Connect your phone to the PC via USB cable
and extract the Auto flash
Run auto_flash_recovery.bat
Reboot your phone
Copy supersu zip to your phone
Boot your phone in boot loader and select recovery wait for a while to open twrp
Flash supersu zip

Done