How does the magnetism strip in stores work?

Answer 1

Do you mean the horizontal holder that they put on the wall to display knives on with the knives sticking there?

It has two long magnets with an isolation gap between them. When you put a knife blade so that the blade touches both strips, magnetism of one polarity (say north seeking for instance) goes into the blade and exits at the other strip (say south seeking for instance). That magnetic force is what grips the knife onto the holder.