How much pressure will be exerted on a diver's body which has an area of 10 m2, if the water column above him weighs 120,000 N

The pressure will be 12000 N/m2.

That is, pressure is the division between force on a surface and the area of that surface.

So, pressure = force/area

If the force is 120000 N and the area is 10 m2, the pressure is 12000 N/m2 or 12000 Pa (pascals) which is pressure unit o measure.