That depends if you already have used one of your travel days in your home country or not. The trip you describe will use 2 travel days in Italy.

If you are a resident of Italy you can travel on 2 different days (00.00-23.59 CET) in Italy.

thank you so much

can I do the follow?

Rome- Venice

2 days in Venice 

Venice-Wien

Munich -Milan

2 days in Milan

Milan-Rome

thanks!

No, that is not possible. That will be 4 travel days in Italy and you only have 2 travel days in your home country. 

Ok thanks

Can I do Rome Venice

2 days in Venice

Venice Wien

Munich Milan?

No, 

1. day Italy
2.  day Italy-Austria
3. day Germany-Austria/Switzerland-Italy

3 days in Italy → max. 2 days in Italy. Interrail is to travel in other countries and not in your country. One day you have to pay a normal ticket in Italy.