How can we measure the Gravitational field intensity of any place on earth ?

Answer 1

with a simple pendulum
period of pendulum = 2 pi sqrt (L/g)
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with a scale

Using a 1 kg weight

force down on scale = m g

in Newtons, weight = mass in kg * g

so g in m/s^2 = weight in newtons / mass in kg

Of course your scale is likely to show kilograms on the dial so assume some standard g of perhaps 9.81 m/s^2

for example if your scale reads 1.2 kg with a 1 kg mass on it
that means
then your local g = (1.2/1)9.81

That means you are standing on a huge Uranium mine I suspect :)