It doesn’t know anything about where it “needs” to go. One of the weirder and more unintuitive things about molecular biology is just how fast everything moves inside a cell. The CRISPR molecule diffuses from one side of the nucleus to the other in a couple seconds and probably bumps into the entirety of the genome in a matter of minutes or hours. It’s very, very crowded inside cells, proteins and DNA and metabolites are constantly bumping into each other and are tumbling around at frankly incomprehensible rates. So, nothing needs to “know” where it needs to go, it simply gets pushed and jostled around until arrives there and then the attraction between the CRISPR’s RNA and the DNA takes over