@ istvan....In the 1980s and '90s I used the book "Städteverbindungen" all the time while traveling in (west) Germany and then in the reunited Germany. It was a book available at the "Reisezentrum" for a small price (5 DM) and sometimes in Amer. Express offices, where it was free. I got one there one time.
I don't know if the book still exists but the little schedules certainly do in the Reisezentrum. You can inquire at a Reisezentrum about the book. The little schedules are located on a rack, lots of them, showing from city X to city Y, accessible for those inquiring, as I pointed out by some examples above. You don't need to ask a DB staff person.
I hardly ever use them now. When I want to get from place X to place Y, I just look it up using the DB ticket machine to get the latest info, say the night before for a day trip from Hamburg to Cuxhaven, on departure times, how frequent the trains run, the connections and times, what type of trains, (IC, ICE, RE, etc), and obviously, the price so that I can decide to pay by inserting the US credit card plus punching in the PIN or putting in cash.
RE these little schedules: people still use them. Like the book (back then), these schedules are all written in German. They're free.