The Holocron was broken into three pieces, each located on a different planet. One piece was located on Tatooine, another on Christophsis, and the third piece on Rodia. Dooku obtained the part on Tatooine, but was stopped on Christophsis by Aayla Secura and an unknown Padawan, and on Rodia by Kit Fisto and the same Padawan.
However, Dooku was able to use the piece he had by harnessing the volcanic energy of the planet Behpour. By channeling the energy into the Holocron piece, he could make it as powerful as a complete Holocron.
The Padawan and Yoda defeated Dooku and recovered the Holocron before Dooku could make use of it. It is unknown what happened to the Holocron after that.
- Didj Star Wars: Jedi Trials (First appearance)