From Longman Dictionary of Contemporary Englishgoodness (only) knowsgoodness (only) knowsspokenNOT KNOW used to emphasize that you are not sure about something, or to make a statement stronger That bar’s been closed for goodness knows how long. Goodness knows, I tried to help him! → goodness
Examples from the Corpus
goodness (only) knows• The last bridge cost $30 million, and goodness knows how much a new one will cost.• At the mercy of wild animals and insects and snakes and goodness knows what horrors!• I suppose that ferrets are no more unusual as pets than rats, snakes and goodness only knows what else.• They took furnishings, china, sofas, televisions and goodness only knows what else.• But goodness knows, Nona had had her say there.• For aficionados those shortcuts are still there - it's still Control+KQX to quit - goodness knows why.• It seems you've survived, goodness knows how, for really it would not matter if you did not.• Though goodness knows why they think they have to do it so early in the morning. 