For myself, I obtained this while taking part in the Whole Cake Arc near the end, playing as Brook. However, as I stated in the previous gallery unlock trophy, you should get the majority of this through simply playing the Dramatic Log. Entries in the character passages, crew log, event viewer, and others will fill in automatically as you come across them, and once you've completed the Dramatic Log, you may have a few music inserts left to unlock through some episodes and then the majority of the gold and rare silver coins. Work on this last if you still need it after Dramatic Log, though I highly doubt you will.