Please check with a native speaker if "How many songs do you know?" is also a correct translation for this sentence. This was my first intention for translation but I did not tried to use it in the placement test as the program seem to go more for word-by-word translation.
(not native) I have seen "nummer" used for "song" online so I would say it's correct. But "number" can also refer to a single song in English as well, so in the right contexts, it might not be necessary to translate this sentence using "song".