How much does an inexperienced waiter make in Milan, Italy?

Not much. Nothing at all if they don't have an Italian passport and speak the language fluently. 

For a start - have you got all the legal bits in place? Visa, permission to live in Italy, etc. Do you speak Italian well?  

Have you investigated the job market for waiters in Milan? I imagine that hospitality in general is a rather slow business at the moment, with Covid restrictions.

a.) Americans are currently banned from entering Italy due to Covid. 

b.) you need a visa and Permesso di Soggiorno to even think of working here.  and good luck getting that....with no contacts already here. 

c.)  unemployment is thru the roof, even for Italians.  Straniere.....forget it. 

In order to legally live and work in Italy, you first need to get a visa that allows that. You cannot just show up there and get a job. See the consulate website that has jurisdiction in your state for details. The consuolate website for Chicago is here: https://conschicago.esteri.it/consolato_chicago/en... . When I got my visa, it took eight months even though it was for the transfer of the job I was already doing in the US.

Note that US citizens are not currently permitted to enter Italy due to the high infection rates in the US.

Without a visa you aren't living in Italy. Without a "real" job there will be no visa. You can do it on your Italian heritage but that will take at least a year. The days of Americans bumming around Europe doing bad table service are long, long past

Read this:https://www.expatsinitaly.com/

Because Milan offers more opportunities than other Italian cities, you should be able to make a start, renting a room, living frugally, as an inexperienced waiter.