From Longman Dictionary of Contemporary EnglishI (only) wish I knewI (only) wish I knewBritish English spokenNOT KNOW used to emphasize that you do not know something, and you wish you did know ‘Where on earth have they gone?’ ‘I wish I knew!’ → wish
Examples from the Corpus
I (only) wish I knew• Don't ask me what I do want. I wish I knew.• Men clustered and chattered lively in groups. I wished I knew how to smoke.• But being so weak seems wrong now too. I wish I knew judo.• I do know that it was because of an argument that he left. I wish I knew more.• He was a sad person underneath. I wish I knew what he was so sad about.• I won't listen to you any more. I wish I knew what time it was.• Very grand. I wish I knew where it is now.• And I wish I knew why. 