Thank you @György-Farkas for detailed answer.
I've tried this ADC (on demo board) on Arduino and also received nothing.
I think that this board is broken.
I bought ADS1115 and now I can smoothly read from photodiode :)

If somebody will need that in future guys from Control Everything Community made working python example for Omega2.
(or at least it's working in my case with FW: 0.2.0 b191)