As posted in the second message on this thread, Ó Muirthile's edition, as reproduced at the Foclóir Na Nua-Ghaeilge website, does indeed give the spelling 'chnocáinín.'
Unfortunately, so does Mánus Ó Baoill on page 39, in Ceolta Gael 2.

The brothers De Barra, however, agree with Felipa. It is from their recording that I encountered the Cill Mhuire song, words and music both; and on their CD album, "An Caitín Bán," their spelling is "Cnocáinín Aerach Cill Mhuire."
Regrettably, I know of no online file for any tracks from their album, #DEBCD001, which I bought from online retailer CD World Ireland.