I am wondering that if the 100% efficiency of the electrolyzer indicates the theoretical maximum efficiency an electrolyzer can achieve because, assuming the hydrogen load is in kg/day not kWh/day, the energy content in the produced hydrogen under 100% efficiency seems to be lowe r than the energy input, so I would like to know if any necessary energy loss is alreay included in the calculation.  And if so, I would like to know the energy loss in percentage.

No, the electrolyzer efficiency is the standard energy-out-divided-by-energy-in.  It's in terms of upper heating value, rather than lower heating value.