How to access DP Aux I2C

I want to communicate with other devices by DP Aux I2C , which SDK should I use?
I use the i2ctest sample code in NVAPI SDK, but it report that" NvAPI_EnumNvidiaDisplayHandle() failed with status -6". I search my computer and find that there are two GPU, one is Intel GPU , the other is nVidia Geforce.