It can be pickpocketed from Cachino or taken from his desk in his suite inside the Gomorrah casino. This is one of the methods that can be used against Cachino to get him to talk about his plan in the side quest, How Little We Know.
Cachino's Journal documents a couple months of Cachino's activities. It contains a detailed ledger describing many of his business deals over the last few months, including the sales of chems and weapons. It is clear at a quick glance that these transactions are his own personal finances, and this is done behind the backs of the Omerta Family management structure.
He also talks, in great detail, about many sexual encounters with Gomorrah prostitutes, including Joana.
After nearly every off-the-books sale, or sexual tryst he vows this one will be his last.