Maybe it's explained, but I can't remember.
Do I have this right? Gym staffer finds it in the LADIES' locker room. And there was a previous scene where Cox's wife is advised to collect financial information in case a divorce proceeds.
That doesn't explain how Cox's "memoirs" is on the disc, and his wife does not seem the type to frequent a strip-mall gym.
So how did the disc get dropped/left behind at the gym?
Katie burned the financial data to a CD/DVD that also happened to have some part of Ozzy's "memoir" on it. She brought it to her attorney, who gave it to his assistant, probably to print or summarize the financial data. The assistant, a member at Hardbodies, put it in her gym bag, probably to take home to work on. It fell out of her bag while she was in the locker room at Hardbodies. That's where Manolo found it, "just lying there." We, the viewers, discover this when the attorney asks his assistant to look at something on the CD, and she looks in her gym bag and can't find it.
shareWe, the viewers, discover this when the attorney asks his assistant to look at something on the CD, and she looks in her gym bag and can't find it.