The Quintesson Journal was a piece of Quintesson technology.
The Quintessons used these cylindrical data storage devices to hold information regaring their scientific operations and allows them to consult the information for analysis. Unfortunately for them, others don't like what the Quintessons have been storing in these devices.
The Transformers cartoon
One such journal was lost on the Junkion homeworld and a team of Sharkticons were dispatched to recover it, but were fought off by the natives. This particular journal contained a subliminal message that made its receivers become more aggressive and xenophobic. The journal caused the Junkions to turn against everyone; even their allies the Autobots.
During the battle on Junkion, the journal was lost and uncovered by both the Autobots and the Decepticons who learnt that the Quintessons were responsible for trading with numerous worlds by providing the inhabitants with technology that would either destroy the planet or propagate wars, in order to profit from the sales. One such profitable endeavour that was recorded on the journal was the thousand-year engineered war between Zitaxis and Lanark. After the Quintesson plot was exposed, the war ended with a tense peace.
Marvel UK comics
The Quintesson Journal was basically a report by Quintesson explorers as to the viability of colonisation of a number of machine worlds across the galaxy. Invariably these machine worlds were already occupied by sentient species (such as Cybertron). The report was created in response to the threat of Quintesson's destruction as its orbit faltered and it began to fall into its sun.
Accidentally jettisoned on the planet of Junk, Wreck-Gar recovered the journal and secreted it in a remote asteroid belt. Captured by the Quintessons, he refused to divulge the journal's location (and, interestingly, gave a false account exactly on foot with that described in The Big Broadcast of 2006). Escaping the Quintessons, Wreck-Gar made his way to the hiding place of the journal and transmitted its contents to the galaxy at large. As a result just about every machine-based sentient species in the galaxy was turned against the Quintessons, virtually ensuring their extinction combined with the destruction of their homeworld.