/usr/lib/x86_64-linux-gnu/pkgconfig/atk.pc is in libatk1.0-dev 2.4.0-0ubuntu1.
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 7 8 9 10 11 | prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=${prefix}/include
Name: Atk
Description: Accessibility Toolkit
Version: 2.4.0
Requires: gobject-2.0
Libs: -L${libdir} -latk-1.0
Cflags: -I${includedir}/atk-1.0
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