You have to book by the internet site

You don't need a reservation for the EC Italy - Munich via Brenner. You have only to buy a 10€ fee at tickets.oebb.at or at any ticket counter of DB, ÖBB or Trenitalia (reservation free on top at Trenitalia). It should also be possible to pay the fee on the train.

->https://tickets.oebb.at/ search munich - venezia and choose as pessenger discount Interrail/eurail so you can pay the 10€ fee.

You can also buy a reservation for 3€ at tickets.oebb.at or for 4€ at bahn.de, choosing I want only a seat.

The site in question is www.oebb.at. Enter your dates, select the direct train, then click “Change” in the box marked “Who is going?”, to add in the passenger details.

Underneath each passenger now listed, click “Add discount”, and type in the search box to add an Interrail pass.

Once you’ve done that, click “Next” at the top right hand corner of the screen. Now you can click “Add to basket” to buy only the surcharge, or scroll down beforehand to add a seat reservation and/or upgrade to 1st class (only if you have a 1st class pass).

@Rebe 

Which Train? the daytrain? or the Nightjet?

Both can be reserved online
the daytrains via bahn.de or oebb.at
the  Nightjet only at oebb.at (special way to reserve)

I´ve made a post with a manual (note there is a daytime manual and a Nighttrain manual for Oebb.at)

Please note that on  the daytrains a surcharge of 10€ (2nd Class)/15€ (1st Class) per person applies (the surcharge is compulsory) The reservation is a extra service and not compulsory for this train but recommened as it´s a popular route  You can avoid the 10€/15€ fee by useing Regionaltrains in Italy :)

Hello ! I face issues to buy a ticket reservation on OBB website about a Venezia-Munchen trip (a Nightjet which leaves on the 22nd of january at 21:05 and arrives on the 23rd at 06:29). I can only buy the ticket and not only the reservation, as I would like. What can I do ?

Thank you in advance for your advices,

Marie POMME

Do you have chosen as discount Interrail/Eurail Pass? Seewulf has done this tutorial how to get reservations. In your case you need the Nightjet Reservation on tickets.oebb.at

i still can find reservations just select Standard & Daytickets even if you wanna reserve and add then in the traveler details Interrail/Eurrail as discount type Then you find reservations from 14€ for a seat :)

Hello,

Thank you for your answers ! It helped me a lot, and I found the solution. It works for the seats, but I guess I have to pay more for a berth ?

yes you have to pay more fore a couchette or a sleeping car. You can change accommodation during the booking on the website. 

Yes, couchettes are more expensive and beds again more expensive.

If you go through the steps indicated in seewulf's manual, then you will get to the step where you can choose what you want to book. If that doesn't work for you, then please indicate where you get stuck.

I finally understood it, thank you very much ! :)