kW is kilowatts. It is a measure of power. hp or horsepower is another measure of power.
Electricity is metered in kWh, a measure of energy. The energy is the power multiplied by the time, so a 1 kW load for 5 hours is 5 kWh.
208 V is the normal phase to phase voltage on a 3 phase system where the phase to neutral voltage is 120 V.
The power in this case is 3 x 120 x 21.2 = 7632 W which almost exactly what the rating plate shows.
I would say that the 35 Amps is just a peak load and can be ignored if you want to know how much energy it will use.
The device will use up to 7.6 kW, so each hour will be 7.6 kWh. However, it might well use less than that, because many devices don't use their full rated power all the time.