Requirements when transiting Italy

A good start: Have you tried filling out https://www.iatatravelcentre.com/ with your specific travel dates and passport information?

With Covid in place these days, requirements on entry/transit/stay still change quite frequently. Even though people wrongly believe vaccine passports (or digital green certificates) allow them more freedom of movement on air travel, this is not (currently) necessarily the case. To properly answer your question, we would need exact route, airline, dates of travel, the passport and the type of passport you intend to travel at least.

To provide an answer which most likely helps you further in your planning, I've assumed the following (today, 2021/07/21):

Arriving in Denmark on 2021/07/24, transiting through Italy on an Air Italia flight arriving from Albania on 2021/07/23 at 16:00 with onward travel on 2021/07/24 at 08:00 after change of airport in Italy, using a "normal" biometric Danish citizen passport which does not expire within the next six months, having an onward journey ticket out of Italy to Denmark.

You're looking at the following setup/constraints (you still need to check airline and airport-specific constraints):

Summary

Yes, the documentation you hold is sufficient based on your details and the itinerary provided.

Passport Denmark

Warning: Passengers are subject to a COVID-19 test upon arrival.

This does not apply to passengers traveling to Greenland.

This does not apply to passengers with a positive COVID-19 PCR test result issued at least 14 days and at most 12 months before arrival. The test result must be in Danish, English, French, German, Icelandic, Italian, Norwegian, Spanish or Swedish.

This does not apply to passengers with a COVID-19 vaccination certificate issued in Albania, Andorra, Australia, Canada, Chile, Colombia, Israel, Japan, Korea (Rep.), Lebanon, Mexico, Monaco, New Zealand, North Macedonia (Rep.), Rwanda, San Marino, Serbia, Singapore, Switzerland, Thailand, Turkey, USA, United Kingdom, Vatican City (Holy See) or an EEA Member State. The certificate must show that they were fully vaccinated at least 2 weeks and at most 8 months before departure. Vaccines accepted are AstraZeneca (Vaxzevria), Janssen, Moderna and Pfizer-BioNTech. They must not arrive from Argentina, Botswana, Colombia, Costa Rica, Cuba, Eswatini, Iran, Lesotho, Libya, Malawi, Malaysia, Mozambique, Namibia, Panama, Russian Fed., South Africa, Suriname, Tunisia, Zambia or Zimbabwe. Details can be found at https://tinyurl.com/9xbu483d.

Passengers could be subject to self-isolation for 10 days. Details can be found at https://tinyurl.com/9xbu483d.

This does not apply to residents of Denmark with a COVID-19 vaccination certificate issued in their country of residence. The certificate must show that they were fully vaccinated at least 2 weeks and at most 8 months before departure. Vaccines accepted are AstraZeneca (Vaxzevria), Janssen, Moderna and Pfizer-BioNTech. They must not arrive from Argentina, Botswana, Colombia, Costa Rica, Cuba, Eswatini, Iran, Lesotho, Libya, Malawi, Malaysia, Mozambique, Namibia, Panama, Russian Fed., South Africa, Suriname, Tunisia, Zambia or Zimbabwe. Details can be found at https://tinyurl.com/9xbu483d.

Passengers traveling to Greenland must have a negative COVID-19 PCR test taken at most 72 hours before departure. The test result must be in English or German. Details can be found at https://visitgreenland.com/corona-faq/; and

• must have a Personal Location Form (SUMUT) obtained before departure at https://sumut2020.gl/Instructions/EditInstructions; and
• could be subject to a COVID-19 test upon arrival and quarantine. Details can be found at https://visitgreenland.com/corona-faq/.

Health Denmark

This information is for guide purposes only. Other health organisations may recommend alternative precautions.

Vaccinations not required.

Passport Italy

Warning: Until 30 July 2021, passengers are not allowed to enter and transit if in the past 14 days they have been in or transited through Bangladesh, India or Sri Lanka.

Passengers are not allowed to enter and transit if in the past 14 days they have been in or transited through Brazil.

This does not apply to parents of children younger than 18 years who are residing in Italy.

Health Italy

This information is for guide purposes only. Other health organisations may recommend alternative precautions.

Vaccinations not required.

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My recommendation for 2020/2021 (based on well over 100 flights since this Covid frenzy started): unless you're a "professional" frequent traveler that knows all the tricks and even some of the staff at the airports (to help overrule last-minute regulations), I strongly advise against routing challenges and always advise direct flights with reputable airlines in Europe.

I did ZRH/AMS/FRA/MAD/FCO/LHR/CDG/ZRH two weeks ago with "transit" in AMS and FCO on three days. The only place they surprised me was the first class lounge in Frankfurt, which demanded a Covid swab test upon entry because my RT-PCR test was older than 24 hrs. Now my flight back to the US is tricky ;). Many countries do ask for paperwork or offer digital registration, almost none do actually follow up on the influx of data they receive, since I suppose that their systems are just not built up for that amount of data yet!