是who knows? 還是who know? ?

The corret answer ic (who knows)

"Who knows" is correct. "Who" refers to singular that requires to use "knows" as if he knows, she knows, althought who could be a group of people but in this kinda situation, we dont use plural. That's the English rule.

both works,depend on the situation, if there's more than one person,then you use "who know", just one person, you use "who know",

是who knows
凡who,whom,which,everyone,someone,etc.都當是單數名詞