Where can I find a license number for an app?

I bought the app Cocktail a while back and I've used it successfully to help keep my MBP running smoothly. But now I need to install the app. I don't want to buy it again and get a new license number. I wrote that single user license number down on a piece of paper but I've lost that information. Is there anywhere in my laptop, maybe hidden in Library or Preferences, where I can find that valid single user license number for Cocktail?

Thanks

Panther