Yes, you can! To show the number of readers of your book, go here:
https://leanpub.com/YOUR_BOOK/settings/web_page_details
...making sure to replace "YOUR_BOOK" with your book's unique web address.
You can also find the "Web Page" details page under "Settings" on your book's Overview page:
On the "Web Page" details page, tick the box next to "Show the reader count on your book's homepage?" at the top, and then scroll to the bottom of the page and click the "Update Book" button:
The next time you go to your book's landing page, you will see the number of readers displayed in the horizontal information bar, part way down the page, under the book's cover image:
Please note that there us currently no feature like this for courses, sorry about that.