Streetwise is covered on page 263 of the redbook. It covers the etiquette of the city streets. It also lets you find places in the city that only a native would know. With your dagger example, you could probably find "Smith Street" with Streetwise. Or if daggers were restricted in the city, you could use it to find out where they were sold on the black market. Equally you could use it to navigate through a city without ending up in places where you would get robbed. Or you could use it to behave properly in such a place so that you fitted in like a local.
Originally Posted by Zelbinian
As near as I understand it, Streetwise is not a "-wise". City-wise is. It is covered by Wises on page 267 of the same book. Wises are mainly about facts and trivia about their topic. They are pretty open and useful skills. Under particular circumstances, -wises can be used by the players to insert facts into the game. There is a detailed commentary on this and other things in the Adventure Burner. You can also find similar material through searches on the forum.
Inspired by Bobo's Sig
Rule 6 of Kurt Vonnegut's Rules on Short Stories
Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them — in order that the reader may see what they are made of.
from Bagombo Snuff Box.