I am currently using X3 version of endnote. I have a number of reference that are only available currently online. I have the DOI information in endnote but this not enclosed in the reference list in my document.  I am currently using the Harvard style for reference

Does any know how I enclosed this information in my document reference list?


You need to edit the Output Style, Harvard, to include the DOI in the appropriate Bibliography template (presumably the “Electronic Article” template, I assume).  Then make sure that article that is only available online, is also specified as Reference Type “Electronic Article”.  - You could also use the Journal article, but then you need to be much more careful about the link adjacent and forced separation characters surrounding the field name in the output style template.  Remember to “save as” to a new name, and then to reformat the manuscript in question with the newly saved style name.  I recommend that you DO NOT save as the original output style name, as then you have two files of the same name in two different places (assuming you are using X2 or later).