I guess you're trying to book a reservation for the night train Munich - Milan. The best way to do it is via ÖBB using these steps. There are still seats, couchettes and sleepers available.

For Berlin to Venice, could you please mention the departure times of the trains involved?

I can get reservations for the Nightjet from Munich to Milan departing the 21st of April via tickets.oebb.at (booking Turorial by Seewulf)

For your journey from Berlin to Venice you can take day trains (ICE - optional reservation via bahn.de 4€/booking) to Munich and change there for the EC Service to Venice (optional reservation via bahn.de 4€/booking, this means for this 2 trains you pay in total 4€). For the italian part you need to pay a 10€ fee (2. class), you can pay also onboard of the train or via tickets.oebb.at. 

Or you take a nightjet from Berlin to Vienna (from 14€ for a seat via tickets.oebb.at) and change there for RJ service to Vienna (optional reservation + 10€ italian fee).

Or you take a ICE to Munich and then the Nightjet from Munich to Venice (from 14€ for a seat via tickets.oebb.at)

Berlin to Venice. I need to be in Venice on 12 th of  April around 9 o clock in the morning so everything before that is okay. thank you for your answer

one more question. I am a resident of Italy what does it mean i have inbound outbound 2/2 and i used them, therefore, i can not add this travel means?

That means you already have used both your inbound/outbound journeys. You can only use Interrail on 2 travel days in your country of residence.

You can check in My Trip on which dates that was: there will an icon Out/In for the travel days where you used them. If there's any travel day where you think it's an error, then please post a screenshot of the journey(s) you did that day.

hi, thank you for your answer.

So basically it means for 10 days travel i can not exceed to enter or exit more than 2 times. is it correct?

Yes, that is correct. For this night train, there is also a fare for the case that you only have a pass for part of the route, but you'll have to buy that at a ticket office in Germany or Austria or by phone from DB or ÖBB.

what happen i used all my inbound and outbound travel numbers? Is it possible for me to buy eurail pass together with interrail pass? 

thank you

If you live in Italy, then you can only buy an Interrail pass.

If you have used the 2 inbound/outbound journeys, then you can’t use the pass anymore in your country of residence.

Thanks for your help. 

Moderator note: the link '’these steps'’ has been changed back to the original link. 

Attention kranlik  changed the 2nd Hyperlink “these steeps” to a different Website as in the original post of @rvdborgt rvdborgt.