God knows idiom informal
（用于强调不理解或不知道某事）天晓得
used to emphasize that you do not understand something at all or have no knowledge of something at all
God knows where he put the keys! 天晓得他把钥匙放在哪儿了！
"What did he mean by that?" "God knows!" “他说那话是什么意思呢？”“天晓得！”