There would be no bad press for saying nothing. There seems to be some debate whether public CEOs have the right to freely express their personal opinions on certain political issues, with a bunch of high profile cases that would be distracting here; but there's certainly no argument that public CEOs have the duty to express (or even hold) any opinions whatsoever on things that are major political events abroad; Cook responding to all Hong Kong related matters (as far as they don't directly concern specific actions that directly affect Apple) with "no comment" would not get any significant bad press as that's not breaking any taboos or even conventions.
