Why a registrar abroad wants this sheet
Before a foreign registrar marries you, it wants proof that Italy holds nothing against it — no live marriage, no pending case. That is all this certificate says. Working out how to legalize a Certificate of No Impediment is therefore the last errand of a wedding file, not the first.
At the Comune counter
The registry office of your Comune prints the sheet while you wait, in a good week. Take photo ID and the exact spelling of both names as they stand on your passports. Read the printed sheet before you leave the desk, because a correction made later restarts every stamp that follows.
The Prefettura, then the consulate
A town-hall record is administrative, so the embassy legalization of a Certificate of No Impediment in Naples starts at the Prefettura rather than the court. Its clerk knows the registrar's signature and stamps the sheet against a specimen on file. The consulate of your wedding country then signs on top, and that pair of stamps is what the registrar abroad reads.
Cost and the calendar
There are two payments and one hard deadline. To legalize a Certificate of No Impediment in Naples you need a €16 marca da bollo on the file, plus the consular fee the mission sets. Normal handling runs 10–15 business days, express 3–5. Book the ceremony far enough out that the sheet is still young when the registrar opens it.
The part nobody checks in time
Two things sink wedding files. First, whether that last stamp is wanted at all rests on the destination; confirm with the receiving authority in writing early. Second, the consular legalization of a Certificate of No Impediment in Italy has to be booked, and slots near summer go fast. The embassy attestation of a Certificate of No Impediment in Naples is quick work at the counter. Getting in front of that officer is the slow part.