/usr/share/denemo/actions/lilypond/ukulele-fretboards.ily is in denemo-data 2.0.2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | \include "predefined-ukulele-fretboards.ly"
\layout { \set Staff.stringTunings = #ukulele-tuning }
|