You can temporarily changed to the numbered output style? – Alternatively, Endnote makes a temporary group that collects the cited references, just below the “all references” choice.
This feature was added in at least EndnoteX7. Attached is a screen shot, for the paper “Document1” – you do need to either add another citation or “format bibliography” after opening the document, to allow endnote to collect the records in the group.
Yes, as I suggested earlier. – format the thesis with the “Numbered” format. this will show you how many cited papers you have. Then you can reformat with the orginal output style. You can even make a copy of the output style you are currently using and add a “bibliography number” to it, and switch back and forth between the two.