Very little if any. Only the clergy, notaries, and a few wealthy individuals (mostly royalty) had any knowledge of Latin at the time. Peasants living in the Italian peninsula were not yet considered "Italian" in the sense that we understand today. The peninsula didn't become a unified "Italy" (nation) until 1861. For centuries, "Italy" was divided. Italian culture tends towards provincialism where people show allegiance to their "campanile", or local church tower, instead of the "state." In 1100, dialects were (and still are) so wildly different from one another that people from Rome or Tuscany or Sardinia could not understand one another. In other words, "Italian" peasants didn't understand Italian anymore than Latin at the time, as Italian became developed in the 1200s as was considered "crude" and only appropriate for a female or impoverished audience. Dante and Boccaccio later revolutionized "Italian" in the 12 and 1300s by writing directly in Italian (derived from the Tuscan dialect). Even if some of the Latin vocabulary was similar to the budding "Italian" of the age, it would still have been unintelligible to peasants who spoke thick dialects whose pronunciation was influenced by Spanish, Arabic, etc etc (Italy was invaded by several cultures for centuries so contemporary standard Italian has many influences.

Sardinian/sardo is the language closest to spoken latin today. Many words and much structure is the same. I would say yes for some of Sardinia!

I may have misunderstood your question. I was pointing out that only the priests knew what was being sad, so the Italians did not understand it, just like churchgoers of different countries.