My security officer has some worries about the license on Contentment. Snyk is reporting a license issue and we're reading things about having to make our source code public. Can somebody tell me how the license on contentment works? Do I need to make my whole website source public when I use Contentment?

As I understand the license, you are only required to release the source code if you modify anything in Contentment. Using it in your own project is permitted as long as you don't modify. https://github.com/leekelleher/umbraco-contentment/blob/develop/LICENSE