He works in both union and pwh...For pwh I don't know whether he take private case or not (pwh also have private clinic in pwh block EF 2/F)
But I am sure that many of his client in union if they run out of money, Prof Mok will refer them back to PWH for futher management. Some public hospital didn't take cases from other region (cluster) but PWH did accept cases from all region.
Of course you can not choose Dr in PWH (if not private case). And also Pro Mok not seeing patient everyday in Pwh... So you have very little chance to see him there(not in private).