The general info (and instructions on what to do if specific licencing info is not included) lives here:

http://www.cpan.org/misc/cpan-faq.html#How_is_Perl_licensed

"Most, though not all, modules on CPAN are licensed under the GNU Public License (GPL) or the Artistic license and should be stated in the documentation that accompanies the module itself. If the license is not specifically stated in the module, you can always write the author to clarify the issue for you."