The general easy method is to view the module's page at MetaCPAN and follow the "issues" link in the left nav. This will take you to the preferred issue tracker for that module. Most often this will be the relevant page under https://rt.cpan.org but could also be an issue tracker at SourceForge, GitLab, GitHub, etc. Recently there has been a push for the CONTRIBUTING.md file in the dist to contain this information as well, so you might look there in preference (this is the "How to Contribute" link in the MetaCPAN nav).
The one notable exception to this is Marc Lehmann's modules. If you raise an issue in this way with him he will ignore it and instead send you an automated reply telling you in no uncertain terms that you should use his private system for raising issues instead. Consider yourself forewarned.
