iCloud enabled in GoodNotes:
If iCloud is enabled (in Options > Settings > iCloud), then your documents and categories will be downloaded to the other device when it is logged into the same iCloud account and iCloud is enabled in GoodNotes.
iCloud disabled in GoodNotes:
If iCloud is not enabled, then your documents are stored locally. If you use iTunes or iCloud to backup your iPad, the data in GoodNotes will also be backed up. Then you can restore a backup to your new iPad and your documents in GoodNotes will be available automatically. For more information, please take a look at this article from Apple.
If you don't want to restore device backups from iTunes or iCloud, please follow the instructions in this article instead.