Analog Input >> General Properties >> Signal Conditioning >> Probe/Attenuator >> Attenuation Value

NI-DAQmx C Properties

Analog Input >> General Properties >> Signal Conditioning >> Probe/Attenuator >> Attenuation Value

Data Type: float64
Description: Specifies the amount of attenuation to use.

You can get/set/reset this property using:
  DAQmxGetAIAtten
  DAQmxSetAIAtten
  DAQmxResetAIAtten