/usr/share/thumbnailers/pentobi.thumbnailer is in pentobi 11.0-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [Thumbnailer Entry]
Exec=/usr/games/pentobi-thumbnailer --size %s %i %o
MimeType=application/x-blokus-sgf;
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