/usr/lib/mono/2.0/Npgsql.dll is in libmono-npgsql2.0-cil 3.2.8+dfsg-4ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/2.0/../gac/Npgsql/2.0.0.0__5d8b90d52f46fda7/Npgsql.dll
/usr/lib/mono/2.0/../gac/Npgsql/2.0.0.0__5d8b90d52f46fda7/Npgsql.dll