there are no reclining seats on this train - just regular 6 seat compartments, which are not very comoftable. Currently, if I book the train 4 days in advance, only seats are left - during peak summer it might be booked even earlier.
Anyway, you can get online reservations for this train, check the link (UPDATE) in the first post of this thread. Attention, for online reservations on CNL trains at least departure or arrival station have to be in Germany. This means you should get your reservation from Emmerich or Duisburg to Kobenhavn, not from Amsterdam! Anyway it shouldnt be a problem to enter the train in Amsterdam with this reservation, just explain this to the conductor. As the reservation cost is the same for any destination all should be fine.