/usr/share/X11/xkb/symbols/empty is in xkb-data 2.10.1-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | default partial alphanumeric_keys modifier_keys
xkb_symbols "basic" {
name[Group1]= "Empty";
};
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