This curve tells you that this Peltier can move 20W from cold side to hot, against a 40C temperature gradient. Or 160W against a 20C gradient. Or 300W, but the cold side will reach the same temperature as the hot side.
So the cooling setup on the hot side determines the hot side temperature for any given power dissipation. Note the power dissipation is not just the pumped power, but the sum of pumped power and electrical power (apparently 48V * 13.6A or 650W).
Then use this table plus the specifics of what you are cooling to determine the cold side temperature.
So if you can keep the hot side to, say, 30C at 650+160W, you can cool something producing 160W down to 10C. Or at 650+20W, something producing 20W down to -10C.
Or given the mass and thermal capacity of the item being cooled, you can determine how the rate of cooling declines as the temperature falls.