You can't. Although the shell of the Apple Pencil is made of metal, it is not magnetic, so it cannot be adsorbed on metal surfaces.
Unlike this, some other brands of stylus may have magnetic components installed on the housing for easy adhesion to the metal surface. However, for the Apple Pencil, in order to be fixed on a metal surface, you need to use a special bracket or clamp.
Yes, some of the metal is the same as the iPad frame metal, you can adsorb.