Here's a list of text variables you can use in Motion to write data in Final Cut Pro:
@#$sourceObject_alphaHandling
@#$sourceObject_angle
@#$sourceObject_audioChannelCount
@#$sourceObject_audioSampleRate
@#$sourceObject_contentCreated
@#$sourceObject_displayFormat
@#$sourceObject_displayName
@#$sourceObject_effects
@#$sourceObject_frameDuration
@#$sourceObject_frameSize
@#$sourceObject_metaData_reel - Source Reel Name
@#$sourceObject_metadataAudioRoles
@#$sourceObject_metadataDeinterlaceType
@#$sourceObject_metadataFieldDominanceOverride
@#$sourceObject_metadataImportToApp
@#$sourceObject_metadataLocation
@#$sourceObject_metadataMediaDuration
@#$sourceObject_metadataMediaEnd
@#$sourceObject_metadataMediaStart
@#$sourceObject_metadataRoles
@#$sourceObject_metadataRotationAngle
@#$sourceObject_metadataSelectionDuration
@#$sourceObject_metadataSelectionEnd
@#$sourceObject_metadataSelectionStart
@#$sourceObject_metadataVideoRoles
@#$sourceObject_notes
@#$sourceObject_objectName
@#$sourceObject_projectOrSource - Source Clip Name
@#$sourceObject_projectOrSourceName
@#$sourceObject_reel
@#$sourceObject_sampleDuration
@#$sourceObject_scene
@#$sourceObject_sequenceName
@#$sourceObject_shot
@#$sourceObject_sourceName
@#$sourceObject_timecodeFrameDuration
@#$sourceObject_timeRange