At any rate give it a listen and take your guess what Shatner's line was supposed to be or perhaps the 23rd century knig of Italy had knighted D'Amato!
The highest ranking honour in Italy is "Cavaliere di Gran Croce Decorato di Gran Cordone Ordine al Merito della Repubblica Italiana" (Knight Grand Cross with Collar). Usually you use the form "Cavalier Rossi" ("Knight Rossi").
There is no title in Italy that you can translate with "Sir". We are a Republic after all
Probably in the 23rd century the House of Savoy had reclamed its rightful throne!
Either that, or they simply decided that to say his title correctly would need a two-parter!
I love the Italian language, can't speak it for crap, but it's one of those that seems to "flow".
Why assume D'Amato is from Italy? It's the 23rd Century. I know plenty of native born US citizens that have thick accents. Perhaps Sir D'Amato is from a country (or colony planet) that has a Monarchy that uses the honorific Sir and his parents spoke American English.
Or perhaps there was some inside joke among the crew that Kirk was aware of but we aren't.