You may wish to add a custom block that appears on all single course pages in your Moodle site.

This is definitely possible, and quite simple to do.

Follow the steps below to add a custom block to all course pages in your Moodle site:

1. First, start on the frontpage of your Moodle site. Make sure that editing is turned on, and click "+ Add a block".
2. Once the block has been added to the page, click the settings icon, and click "Configure". 
3. On the block settings page, under "Where this block appears", select "Show throughout the entire site".
4. Next, open up one of the existing courses on your Moodle site (it doesn't matter which course).
5. Now, click the block settings icon on the block again, and click "Configure".
6. Under "Where this block appears", change the setting to "course-view-*.

Following these simple steps will allow you to create a block that is shown on all single course pages throughout your Moodle site.