Answer
$1.11\;\rm nC$
Work Step by Step
Since the copper is a conductor and since the potential inside the conductor is the same everywhere else on the same conductor, the potential of the surface of this copper sphere is also 500 V.
Thus,
$$V_{\rm surface}=\dfrac{k_eQ}{R}$$
Solving for $Q$,
$$Q=\dfrac{V_{\rm surface} R}{k_e}$$
Plug the known;
$$Q=\dfrac{(500)(0.02)}{(9\times 10^9)}$$
$$Q=\color{red}{\bf 1.11}\;\rm nC$$
