Not thick but lacking in confidence.
2000 Watts means that the kettle supplies 2000 J of energy every second.
You can calculate the heat needed to boil the water if you know the starting temperature of the water and as long as you know that every g of water requires 4.184 J to raise its temperature by 1 oC.
Then heat energy required (J)= Mass of water (g) x change in temperature (oC) x 4.184 (J/oC g)
Assume the starting temp is 20 oC then change in temp is +80oC ( 100 - 20 oC)
Then heat required = 1000g x 80 oC x 4.184 J = 334720 J
But you know the kettle provides 2000 J every second so
Time taken = 334720 J / 2000 J per s =167.36s ( 2 mins 47s)
Obviously, if the starting temp is not 20oC you will need to make a minor adjustment to the calculation but i am sure you can do this.
initial temp of water say 15 C to be raised to 100C = 85 C
1K x 85 x 4200 divided by 2000 = 2.975 nearly 3 minutes
if the water is at 4C it will obviously take longer
John's answer is good if you meant how long it takes to bring the water to a boil.
If you meant how long it takes to boil it away, then you need the latent heat of evaporation too.