To find out how widely referenced a book is, turn to Google Scholar and a database called Scopus. Neither is comprehensive, however; you will see different results for each method, which reflects the difficulty of actually taking a comprehensive citation count. But on to a closer look.
Google Scholar has the "cited by" feature, through which you can tell how many times a particular piece of material has been cited.
At the time of writing this FAQ, Braiding Sweetgrass has been cited 4586 times, according to Google Scholar. Note: the URL to the right you may also see a Google Books link, which will give you a different figure for total citations.
Scopus is an abstract and citation database. It lets you search for articles, authors, or journals and sort your results by the strength of citations. In your case, it will allow you to examine the number of citations and the citations themselves for a particular book. Access Scopus from the A-Z database list. On the Scopus homepage, click the dropdown menu for "Search within" and enter "References". In the "search documents" box, enter "braiding sweetgrass". You'll see a list of documents pop up, telling you the number of documents with a reference list within which Scopus has been able to find the term "braiding sweetgrass".
As noted, this is an imperfect process. Scopus shows us that Braiding Sweetgrass has been cited 1600 times, very different from the Google Scholar number. This could be due to the imperfect nature of the Scopus search - Scopus is generally better at articles than it is books, and I've only searched for that exact term appearing in the references anyway, which means there could be articles that contain that term (perhaps referencing the book) cited as well.