You can calculate watts from kilojoules and seconds, but you can't convert kilojoules to watts, since kilojoule and watt units represent different quantities.
The power P in watts (W) is equal to 1000 times the energy E in kilojoules (kJ), divided by the time period t in seconds (s):
P(W) = 1000 × E(kJ) / t(s)
watt = 1000 × kilojoule / second
W = 1000 × kJ / s
What is the power consumption of an electrical circuit that has energy consumption of 9 kilojoules for time duration of 3 seconds?
P(W) = 1000 × 9kJ / 3s = 3000W