The Online Discussion Forum has a range of options for when you will receive notifications to forum topics. Notifications can be requested at the "Category" level, or at an individual "Topic" level.
To be notified whenever a comment is made for any topic in a category click the bell shaped icon at the top left of the page when you are browsing the list of all topics for a category and choose Watching.
If you want to follow one or just a few topics in a category, select the topic you are interested in and click on the bell shaped icon at the bottom of the topic and choose Watching
Select Muted to stop receiving notifications on a topic or category.