Open Find Font panel on type menu, there you cand find missing fonts and replace.
There is no way to automatically select missing characters. However, that's not a problem because it is Not What You Want. What You Want is to apply a font that supports CJK to these CJK characters (only). The easiest way to do so – automatically! – is with a GREP style.
This has been asked and answered before, but I cannot easily locate the relevant discussion. Quite possible, my own local Search For Chinese GREP was a result of it: