How to get the path in file of a different file of the module?
There is no such thing as a "another file of the module". A module would represent only a single file; a distribution represent multiple modules and thus multiple files. Additionally a module cannot assume it is being loaded from a file system -- it might be loaded into memory out of a tar file or socket, and if a module were to try to access e.g.
"../MyOtherModule.pm6".IO it would obviously fail.
What you can safely do is get at the content of any module in the same distribution:
unit class Aaa::Bbb::Ccc; my $bin-code = $?DISTRIBUTION.content("bin/app").open.slurp;