Analog Input >> General Properties >> Digitizer/ADC >> Resolution Value

NI-DAQmx C Properties

Analog Input >> General Properties >> Digitizer/ADC >> Resolution Value

Data Type: float64
Description: Indicates the resolution of the analog-to-digital converter of the channel. This value is in the units you specify with Resolution Units.
Restrictions: Not Settable

You can get this property using:
  DAQmxGetAIResolution