What is the force on the body on earth?

Depends on the mass/weight of the body.

However, gravitational acceleration is 9.8 m/s^(2) .

then remeber the equation.

F = ma

Force equal mass multiplied to acceleration.

Since we know the acceleration is 9.8 m/s^(2), we need to know the mass of the body, inorder to calculate the fore (F) on that body.