If you lack an account, go to the Java Bug Database -- https://bugs.java.com/bugdatabase/, and about halfway down, you will find options for submitting a bug or a Request-for-Enhancement (RFE). You check some boxes, fill out a form, and press submit. Then, a member from the Java team or Java's bug reporting team (usually ANUPAM) will get your ticket submitted to the JIRA. They will also email you, notifying you that your ticket was approved to be added.
When they notify you, they also provide you a point of contact email. You can can send comments on your ticket by emailing this point of contact email.
And finally, if you want to comment on tickets that do not belong to you, you can reach out to ANUPAM and request them to forward your comment. But they might be hesitant if it is not your ticket.