Giuseppe's Journal is a journal that belonged to Giuseppe Salvatore. The journal presumably contained information about the existence of vampires — information privy to the Town Council only. According to Damon Salvatore, Giuseppe "barely knew how to spell his own name", therefore he doubted there would be anything relevant in the journal.
Despite being a relevant topic at the time, there is no mention of Katerina Petrova in the journal. Nor does the journal mention the tomb, or how to open it — perhaps because Giuseppe was unaware of this, given Emily Bennett secretly sealed the tomb without his knowledge.