Working from this documentation page, I used the settings icon on the dictation interface to create a custom dictionary for dictation. The dictionary is visible when I go to the settings again, and words in it are transcribed successfully. However, the directory
iCloud Drive/Drafts/Library/Dictation
does not exist. Library/ still only contains folders Scripts and Templates.
I tried creating the Dictation folder myself then editing the dictionary from the dictation settings, and also creating a second dictionary, but the folder remains empty.
In Settings > Storage > iCloud > iCloud Sync, Enable iCloud is turned on, and my drafts are synchronising between devices as normal. This is Drafts 54.0.2 at iPadOS 27.0.
Where is the JSON representation of the dictionary?