How to subscribe to the jobs mailing list?

edit

This one https://discourse.ros.org/c/jobs

That is not really a mailing list in the traditional sense, but a Discourse category. I believe you should get notified of all posts to discourse.ros.org by default, but if you just want to receive postings to certain categories, go to Preferences (the little cog icon, top-right in the drop-down menu after you've logged in and clicked on your avatar image), then scroll down to Categories and configure it for the categories that you'd like to watch / be notified about.