Upvote:2
Complementing Tor-Einar's answer, NS International (the international service of Dutch national railways) has a very neat summary on the rules to carry bikes within the different carriers for Belgium, France, Germany and Austria here. The rules for domestic service are here (Dutch only)
A quick summary below - unless mentioned, this is for taking a bike as a bike, not as oversized luggage.
Upvote:4
I am not sure if your question is too broad for this format or are you really just looking for any arbitrary train where you can bring a cargo bike?
If that is your question, you can at least do it on some ΓBB trains (Austrian Railways). Not as a regular bike, but as cargo or oversized luggage in trains which still have luggage wagons or designated luggage compartments. You can't book the ticket online, but have to call ΓBB customer service or go to a ticket counter to make a reservation.
Even if cargo bikes often exceed the allowed size of bikes transported in trains, I would assume that all trains still running with luggage cars allow cargo bikes to be brought under the same conditions as any other oversized luggage.