With the pass you can select on your own which trains you wanna catch :)
Most Nighttrains need a reservation means you have to reserve your prefered comfort level before you catch a Nighttrain :)
How ever the Nighttrain Paris - Venice doesnt exist anymore Current otherway could be a TGV/ICE from Paris to Stuttgart and catch the Stuttgart - Venice Nighttrain :)
Other Nighttrains you may use are Paris - Vienna, Amsterdam - Innsbruck, Prague - Zürich.
The Nighttrains Stuttgart - Venice, Venice - Vienna, Vienna - Berlin, Berlin - Zürich are all operated by Austrian Rail under the brand of Nightjet you can book (ticket & reservations) or reserve (just a reservation on top of a Interrailpass) easily on the website of oebb.at :)
DE=Germany has a fair lot of INternal ICE=daytime trains, seats only, NO RES needed even as such (but advisable for some rest) doing longer runs like from München to Hamburg/RHein-Ruhr area, Berlin to Rh/Rr or FRAnkfurt etc. PKP in PL=POland also does, but here you must RES (thats only 1 PLN for seat=22 cts, more for sleep/couchette-but these are in summer often booked long before travel).