The information probably already seen, available in english on the website of Deutsche Bahn's CityNightLine service:
http://www.bahn.de/citynightline/view/en/service/waehrend-der-reise/speisewagen_menu_reservation_en.shtml
and
http://www.bahn.de/citynightline/view/en/service/waehrend-der-reise/fruehstueck_en.shtml
Also, this is what "the man in seat 61" says about it (the pictures on that site seem to be a little outdated though):
"Never assume there will be a restaurant car, unless you are specifically told there is. On the early-evening City Night Line departures from Paris or from Amsterdam there is definitely no restaurant or buffet car, so take a picnic and perhaps bottle of wine with you!"
See here:
http://www.seat61.com/citynightline.htm
Bottom line: it seems like there is no dining car serving complete meals. All the bord bistro can do is serve cold snacks (bread like "Vollkornschnitten", very nutritious, still possibly not such an appealing dinner), or heat up a "Frikadelle" or some sausage. A full meal is not available.
Since the departure from Basel is quite early (18.26), one could eat at the station beforehand, though that might be too early of a dinner for some. The other option would be to take some favorite food, some delicious food item that doesn't have to be eaten right away with on the train, like man in seat 61 suggested.
Personal side note: after a moment, I remembered, I took one of these CityNightLine trains, when spontaneously the late-evening flight ended up being canceled, but I had to be at the destination the next morning for business. What else could have been the alternative with no more flights available? After shortly considering a one-way rental and driving all night (more expensive, definitely more tiring), I ended up rushing from the airport to the main station using rapid transit, I was so close in time to the departure that I searched for the conductor on the platform and purchased the train ticket plus economy sleeper compartment right on the platform.
And it was cheaper than I thought it would be, and the BahnCard discount was applied to the train fare part of the ticket. So much better than being in CityNightLine's coach overnight in economy - I know some people can do it, and I envy them, still I did it once years ago and I can't fall asleep for a minute while being seated and thus basically need a day off the next day. So I remember receiving that "breakfast box", that is pictured there on the website, in the economy sleeper back then that morning. It was nice, arriving semi-rested, and ready for business at the destination. Now seeing those deluxe sleeper compartments for the first time on CityNightLine's website: They look nice. Not worth the price to me, but nice!
(End of personal side note.
)
Greencats, what sleeper are you going to book, economy, or deluxe?
Basel to Copenhagen will feature the double-deck sleepers as well...
When are you planning to go?
Are day trains possibly also an option for you? (It's also an experience to go with a whole ICE train onto a ferry on the way to Copenhagen, and have a boat trip as part of a train trip...
)
No matter what train, either way you'll have an awesome time on the train traveling on this beautiful planet...