/usr/share/gnuplot5/pm3d/pts.dat is in gnuplot5-data 5.0.0~rc+dfsg2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6
0 0 1 0 1 2 0 2 3 1 0 4 1 1 5 1 2 4