Displaying a cronological reference number on the user interface ie. right hand pane of EndNote

It is not clear whether you mean chronological in terms of when the reference is added to the library (which can be viewed by going to Edit -> Preferences -> Display Fields and choosing “Record number” for one of the fields) or chronological in terms of where the reference is cited within a Word document.

I think you mean the second, in which case I cannot offer any help, but in case it was the first I thought I would post!