CD Project included a configuration tool in the game files. You can find it in the Bin folder in the game local files.

...\Steam\steamapps\common\the witcher 2\bin\Configurator.exe

Locate and clic the Key Mapping button, then the 'gamepad' tab to access that screen :


Here is the layout that works for me.

Basically light attack and heavy attack are bind to RB and RT, parry to LB, dodge to B, and target lock-on on the right stick.