  Questions about detecting CP-violating decay process of $J/\psi\to
K^0\bar{K}^0\to K_SK_S$ are discussed. Possible background and material
regeneration effect are analyzed. The discussion can be directly extended to
other vector quarkonium decays, like $\Upsilon$, $\psi (2S)$ and $\phi\to K_S
K_S$.
