Digitally variable zener diode reference
Probably R7 should pull up to +12, otherwise it only sees 1.5V Vgs which is insufficient to reliably turn on M2 fully.
However when M2 is on, then the output is reduced by Q4, and why that is included is a bit of a mystery. Also you cannot use a 6.2V reference with a MAX9038 since the maximum power supply voltage is 5.5V and the absolute maximum input voltage (not for functionality) is 6.0V.