Microsoft OneNote

Is there a plug-in Cite-while-you-write for Microsoft OneNote?

No, but if you can save to the RTF format, you can insert (by ctrl-C from endnote to Ctrl-V ( paste) int the document, to create the {endnote “citations”} and then use the “format paper” to open the .RTF document and format the references.  Search for the “RTF file extension” in Endnote’s  Help for more details.