This postcard shows the Overland Limited “observation parlor with library writing desk and stenographic service.” The “library” apparently consisted of the books in the elegant, glass-fronted cabinet and the magazines on top. The “stenographic service” was the typewriter and an on-board secretary able to take dictation.
The white border around the postcard dates this card to 1915 or later. Most cards before 1915 were printed in Germany, but the war led American printers to learn the lithographic processes that the Germans excelled in. To save money on ink, the Americans left a white border around their cards.
The electric fans tell us this car was before air conditioning. Most likely, the card was printed before 1920.
The car shown in the picture below (which is from Wikipedia) is from an earlier version of the train; note there is no white border and Wikipedia says a postmark on the card dates it to 1913. In this case, the “library” is in a baggage-buffet car that is the first car on the train.
The picture below (which does have a white border) shows a close-up of the desk in the older car. In this case, the desk is to the left of the bookshelves, while to the right is probably a connecting door for employees to access the baggage compartment. It is possible that the Overland Limited of the 1910s had a writing desk in both the buffet and observation cars.