You got mustard at the tip of your nose.
That police dog started twitching the tip of its nose and sniffing at the stranger.
When Fugu saw that the tip of Salmon’s nose was so red, he found it very cute.
You know the previous part of your nose? The part of your nose I just chopped off? Well, you were lucky, as that was only the tip of the nose. Time to cut off the rest, next!
The readings are the kun'yomi vocab readings. With 鼻 you learned that with the kanji. With 先 you learned that with the vocab. So, you should have all the pieces to be able to read this. Remember, body parts tend to change words into kun'yomi readings for some reason, no exception here.