How much energy is contained in matter what the mass of 1 gram (0.001 kilogram)

Classically and Newtonianly, it's the sum of the chemical energy if any,
the electrical energy if any, the thermal energy if any, and the mechanical
energy consisting of potential and kinetic energy if any.

The mechanical energy, consisting of potential and kinetic energy if any, is

           0.001 x [ (acceleration of gravity x height) +  (1/2) (speed)² ] .

But I've got a sneaky hunch that you're not talking about any of these.
You want to know how much [ mc² ] there is in 1 gram of mass.  No prob.

           E = m c² = (0.001) x (3 x 10⁸)² = 9 x 10¹³ joules

That's the energy that a 1,000-watt toaster uses
in  2,852 years  of continuous toasting.

Because its reliable.   there is no pollution  the chances of a radiation leak is low