In chapter 1 of Nodame Cantabile, it is implied that Chiaki is playing some Beethoven in preparation for the school concerto competition. We also get a snapshot of a score, which presumably contains what he is playing.
Do we know what piece Chiaki is playing? In the anime, he is playing Beethoven's Piano Concerto no. 5 ("Emperor"), and it is easy to recognise as he starts from the beginning of the first movement. However, the score here does not correspond to any section of the concerto that I can recognise, and in any case, we are not explicitly told what piece he is practising.
I tried skimming through a copy of the piano part of Emperor and could not find a section that matched. Inputting part of this score into the Musipedia search engine also did not get any useful results.