Wiring pH sensor

Hi guys,

i am almost done with the first stage of my project, some sensors already attached but there is one remaining and the most important for me, the pH sensor.

I am a software engineer student, i have only learned the basics on the electronic side and i only have one of these sensor reader, so don't really want to screw things up

The eagle schematic (pdf version)

On the sensor circuit i am able to read GND, VCC, SDA, SCL .

I am paying attention to the ADC schematics and what confuses me is that i don't know what VDD is because is not showing on the circuit board , as it does not show VCC and AIN.

A bit lost here, hope i can hear from you soon as i'm eager to put this running!!

Thank you very much,