I know that electric charge is lorentz invariant quantity and I can easily think of experiment to check that. Is a though experiment that can prove that also?
Rather than on a thought experiment, our assumption of Lorentz invariance of electric charge is based on Lorentz invariance of Maxwell's equations. The latter was the reason for developing the theory of relativity and invariance of electric charge came as a natural consequence. If charge were not invariant, the theory would have to be strongly modified (Maxwell's equations would break down when changing reference frames).