The output is intended to be machine-readable, not human readable. Use a tool such as rapper(1) to convert the data to different formats.
In this mode the output is TriG syntax rather than Turtle, due to the extra GRAPH statements. Some tools which understand Turtle do not understand TriG.
The possible TYPE options are:
files-starred - Export starred files (as created by GNOME Files)
photos-albums - Export photo albums (as created by GNOME Photos)
photos-favorites - Export starred photos (as created by GNOME Photos)
$ tracker export -b org.freedesktop.Tracker1.Miner.Files | rapper - -I . -i turtle -o turtle