venice to berchtesgaden

No need to go to Munich. Go to Salzburg and take a bus from there to Berchtesgaden. The detailed timetables on the German Rail include the bus route.

The link given by Tim gets you to the Bahn Query Page eventually, but you might as well go directly there with this link. There are about five EuroCity trains daily every two hours direct from Verona to Munich. One even originates in Venice (at 13:34). You can connect from that train to an IC in Rosenheim and then change to a regional train to Berchtesgaden in Freilassing. With advance booking, you can get a Europa-Spezial ticket all the way from Venice or Verona to Berchtesgaden starting at €39/p. The route to Salzburg starts with an express bus run by Austrian Rail from Tronchetto in Venice to Villach, then a train to Salzburg. You can book that route on the Austrian Rail website, www.oebb.at. The second of these bus/rail connections arrives at Salzburg Hbf at 17:48, and the last bus of the day to Berchtesgaden leaves from the Hbf at 18:15, so you'll have move fast to catch it. However, the train from Salzburg to Berchtesgaden via Freilassing runs until almost midnight. You can also book one of the ECs from Verona or Venice as far as Innsbruck and an Austrian train from Innsbruck to Salzburg on the Austrian website.