The b5 notes means the flattened fifth note of any scale. If we have e.g. a C-major scale (c – d -e -f -g – a – b – c ), the fifth note is the g , and if this note is flattened, we get the gb. The same logic works with any major or minor (or other) scale.
The following video demonstrates the usage and the position of this note. You will find Mark Knopfler licks from Sultans of Swing (Alchemy version), Calling Elvis, In the Gallery, Down to the Waterline, and many more.
I did not tab these licks here, but I think you will not have problems to see how they are played. Remember, it is not important to play something authentically but rather to understand the idea behind what is being played. Only this way you will be able to transfer the licks into your own repertoire, and to use them for your own music.
The video is in high quality here. If you have bandwidth problems, click here to go to youtube and watch it at standard quality. Enjoy.