§78

Wittgenstein presents us with three cases:
 (i) how many metres high Mont Blanc is.
 (ii) how the word 'game' is used.
 (iii) how a clarinet sounds.
In the first case it seems clear that if you know it then you can say it (if you know how many metres high Mont Blanc is then you can say it).
In the second case - again - if you know it you should be able to say it (although given that it is a family resemblance concept you might have to say a bit more).
In the third case it is less clear that if you know it you can say it. - You would most likely compare the sound to some other sound.

Note: §75 makes it clear that Wittgenstein does not think that (ii) is a case of knowing but not benig able to say it. In this passage we can know how many metres high Mont Blanc is, we can know how the word 'game' is used, and we can know how a clarinet sounds. We can also say how many metres high Mont Blanc is ('Mont Blanc is 4,260 metres high'), we can talk about how the word 'game' is used ('the word 'game' is used to refer to things like monopoly, Halo, football, and poker') and we can say how a clarinet sounds ('it sounds like this [play a note on a clarinet]').

What this passage makes clear is that there are various different kinds of explanations (although it perhaps sounds a bit strange to say that in saying 'Mont Blanc is 4,260m' I'm explaining how high it is).