Dear Luigi Sannuto,
Thank you for posting your inquiry on History Hub.
Naturalization proceedings were carried out by courts until the 1990s (federal, state and local) and the records are held by their repositories. The National Archives holds the records for Federal District and Circuit courts and those are divided by location. To locate your father’s naturalization documents and to request a certified copy of it you can send an email here - https://www.archives.gov/contact ; or, if you know in which court your father naturalized (which should be listed on the certificate) you can send an email to the National Archives location that has those court records. Court holding locations can be found here - https://www.archives.gov/research/court-records
In your request please include the name of petitioner (including known variants); date of birth; approximate date of entry to the US; approximate date of naturalization; where the individual was residing at the time of naturalization (city/county/state); and country of origin.
In most cases, the National Archives will not have a copy of the certificate of citizenship. Two copies of the certificate were created – one given to the petitioner as proof of citizenship, and one forwarded to the Immigration and Naturalization Service (INS).
Certificates of citizenship were issued by the Federal courts until October 1991 when INS took over responsibility for naturalization proceedings. All INS records are now overseen by the US Citizenship and Immigration Services (USCIS). USCIS maintains duplicate copies of court records (including the certificate of citizenship) created since September 27, 1906 and may be requested through the USCIS Genealogy Program.
For more information you may wish to visit - https://www.archives.gov/research/immigration/naturalization
We hope you find this information helpful. Best of luck with your research.