Go to EndNote > File > Share > [Login EndNote online account] . Type the sharee's email and give the permission (read & write / read only) to him / her. This function will share your entire library references as well as attachments with the recipients. If you give the permission of "read & write" to the sharee, the sharee can edit your references and you will get Shared Library Activity Feed.
Note: Require your EndNote account.
EndNote 20.1 will allow you to share with up to 200 EndNote users. Click here for details.