Connecting flights from Italy to China and then to Germany.

If it's a connecting flight of the same airline, you don't have to go through customs. When you are in Rome, the airline will change two boarding passes for you. Then transfer directly to the customs and take the transfer channel.

As for electronic tickets, you'd better print one for later use. Get ready.

If it's not from the same airline, you just need to change your boarding pass after the luggage goes through customs. Just take the printed e-ticket to the counter and show your passport to check in. No other information is needed. Italy and Germany are both Schengen countries, so you don't have to worry about visas, just like changing planes at home, so don't be too nervous.