How to retreive my DP 6.20 serial/key

Hello,

I have an issue with DP 6.20 and  the HP support ask me the serial number, but I can't found it. My problem is that the installation was done by another person who has left the compagny and I cannot find the licence/key...

Know anyone a command or a tip to find the key of my DP ?

thanks a lot for your answer.