Say I had a laser drill that could cut a 2 km circle. I start it up in the deepest part of the ocean. I would then be cutting a 2 km circle straight for the earth core but just before I hit the liquid core. I shut off said drill. What would happen to the liquid ocean water at that pressure as it fall back in.
Do you mean "you can remove a cylinder of material going all the way through the Earth, letting water go down?
If so, well, the Earth should survive. There will be a mighty earthquake. Several things to consider. Earth is liquid inside. So water will not be able to get all the way in. Magma will get there first. Next you will have water overheating at the water/magma surface. Magma will be cooling down. Water is an efficient coolant, so magma will solidify and the heat exchange will slow down.
The exact yield of the explosion depends a lot on how you are going to remove this cylinder. We should wait for a sound explanation how you can do it before we start calculation.
Laser will not work. You probably think of laser as something that evaporates stuff. You don't have any way for steam to escape from the bottom of the ocean, so first, you r laser will have to evaporate all water from oceans. But then, what will be flowing in that hole?
What effects are you looking for? High static pressure? Check experiments in a diamond anvil. Loud boom? Using a laser that can drill a hole in Earth for just that purpose is a waste. Meteorites is your best way to go. You can even use your laser to direct them at/away from Earth. Evaporating material should create enough propulsion.