Noses in manga are sometimes shaded and sometimes not. Sometimes they draw nostrils sometimes they don’t. My point is, that when it comes to manga, as long as it looks good on the character in the spot the nose should be, it’s a good nose. I’ve even seen characters like Krillin from Dragon Ball Z with no nose at all.
It's worth noting that the Creator of DBZ, Akira Toriyama, is arguably not the best technical artist out there - but his ability to creatively rethink the style he’s working with is unmatched. It’s for this reason that he is one of the most successful Manga artists in existence today and that I’ll be referencing him more often than any other artist in this tutorial: because you too should creatively rethink the style in order to really express yourself.