Forget Pan Number

Pan Card is applied by my one of the colleague 4-5 years back but the Pan Card is not delivered to him.  Now he want to apply for Pan card but any document related to this old Pan card is also not available to him.  For applying reprint/duplicate Pan card, any document proof of old Pan card is mandatory.  Please confirm how can he know the number of his old pan card and how can he apply for reprint of Pan card.