Generate JSON file and save to current directory:
plutil -convert json -r -o `sw_vers -productVersion`.json /System/Library/Input\ Methods/CharacterPalette.app/Contents/Resources/Category-Emoji.plist
Generate JSON file and copy to clipboard:
plutil -convert json -r -o - /System/Library/Input\ Methods/CharacterPalette.app/Contents/Resources/Category-Emoji.plist | pbcopy