well first, in NVIDIA control panel, you need to go to the "change resolution" section. From there, you can choose a 10bpc.
But if you're not using the proper connection type, then that might be why you're not seeing any option for changing it.
Also, what purpose do you have for enabling this? You using any programs capable of displaying images or videos that are 10bit?
Cuz with 10bpc, applications need to use DirectX for their render engine since it's directly linked with DirectX on NVIDIA's side of things.
Don't see much in the way of OpenCL/GL supporting 10bpc.
So programs like photoshop are out of the question as far as I can tell.