I need to know if I can find, online of offline, information about the years that census were performed in Italy.
When you are uncertain as to the type of records for an area (and time) and their availability, then the Research Wiki at Family Search is a good place to start.
For an initial search, just enter the name of the country in the search box. In the case of Italy, there are more than 1,000 pages but the second on the list was called Italy Census
On that page you will find
The first census of Italy was taken in 1871. Since then, a census has been taken every 10 years.
Census records up to 1991 are held in the state archive of each province. Census records from 1911 or 1921 to 1991 are also usually found in each comune’s anagrafe (register’s office).
Where to find details of the relevant archive office and anagrafe? Just look for a Research Wiki page for the province.
Well the site that you linked seems to state that Italy doesn't conduct regular censuses, so there won't be any list of dates on which they were held.
Certainly there don't seem to any censuses listed on Ancestry. What there is, and what that site is talking about, is various collections of civil registration information - records of births, deaths and marriages.
A correction to the statement that the first census was taken in 1871 - there is actually an 1841 census online for some regions of Italy. To access it (and many other Italian records from the 1800s), go to http://www.antenati.san.beniculturali.it/?q=gallery Click on your province, then click on the "Stato civile della restaurazione". Many areas do not have census information, but (thankfully for me), mine did.
Here is the cover page from the 1841 census from my area. Click on the "successivo" link near the top right to see some sample pages of the census.
It is possible to look at the coverage for a country on Ancestry's sites without having a World Subscription.
Go to any Ancestry site and on the top navigation bar, choose search. From the drop-down menu, choose Card Catalog. You can filter the results further by going to the menu on the left and choosing Europe, then Italy.
Click on each record collection -- for example, Como and Lecco, Lombardy, Italy, Civil Registration Records, 1866-1936 -- and then scroll down the page until you can see the sections called Source Information and About [title of database]. The source information will tell you when Ancestry put the records online, and where the original records can be found:
Ancestry.com. Como and Lecco, Lombardy, Italy, Civil Registration Records, 1866-1936 [database on-line]. Provo, UT, USA: Ancestry.com Operations Inc, 2008.
Original data: Lombardy Region, Italy, Civil Registration Records, 1866-1936. Tribunale di Como, Como, Italy.
The About section describes the collection and says what kind of information you might find in the records.
By looking through the card catalog, users can see whether Ancestry has any records for the locality and time period needed before they pay for a subscription.
Other websites with genealogy records can be evaluated the same way -- look for a link that will show you a list of records for the site.