You can check if it's in a specific package, but

• I don't know anything that checks if a function exists in any package (so I coded up a solution below).
• I don't know anything that checks if a function is in a module (and that's impossible to do correctly given Perl's dynamic nature).
• I don't know anything that checks if a function is in any module on the machine (and that's impossible to do correctly given Perl's dynamic nature).

In the current package:

UNIVERSAL::can(__PACKAGE__, 'myfunc')
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In a specific package:

UNIVERSAL::can($pkg, 'myfunc')
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In any package:

sub check_for_func {
   my ($func_name) = @_;

   my @pkgs_with_func;
   my $helper;  # Don't combine this line with the assignement.

   $helper = sub {
      my ($pkg_name) = @_;

      my $pkg = do { no strict 'refs'; \%{$pkg_name.'::'} };

      push(@pkgs_with_func, $pkg_name)
         if   $pkg->{$func_name}
         && *{$pkg->{$func_name}}{CODE};

      my $pkg_name_ = ($pkg_name eq 'main'
         ? ''
         : $pkg_name.'::'
      );

      /^(.*)::$/ && $1 ne 'main' && &$helper($pkg_name_.$1)
         foreach (keys(%$pkg));
   };

   &$helper('main');
   return @pkgs_with_func;
}

print(join(', ', check_for_func('test')), $/);
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ikegami++, good reply. The only thing I'd do differently is use the class method syntax for calling UNIVERSAL::can. I think it looks nicer:

    __PACKAGE__->can('myfunc');
    $pkg->can('myfunc');
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Not only does it look nicer (especially with CLASS), but it allows packages and modules to overload can() too.

defined &myfunc
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