The ClinicalKey corporate recommendation does not necessarily follow the citation style guidelines that you may need for your class assignments or for the publication of a manuscript. Since ClinicalKey contains different types of content you will need to note what type of material you are citing in order to follow the style rules for that type of resource.
According to the ClinicalKey User Guide, Viewing and Sharing Content:
Unfortunately, it is not possible at this time to export citations from ClinicalKey into bibliographic management software like EndNote.
How to work around this flaw:
For journal citations, search for these citations in Scopus. Scopus is primarily a journal citation database. You can use the Direct Export option within Scopus to easily send your search results into your EndNote account. To learn more about this option, see the Library's guide to Scopus
For books or book chapters, you can retrieve a record for the book from the library catalog (yes, all then ebooks should be in the catalog!) and the export the record from the catalog into EndNote.