An important consideration when shielding magnets is that the magnets will be attracted to the shielding material. There are no magnetic shielding materials that will not be attracted to a magnet.
Shielding repulsion between 2 magnets is easy:
Use a high saturation alloy like MagnetShield. Simply stack enough layers between the 2 magnets until the attraction to the shield balances the repulsion between the magnets. The proper number of layers will depend on the strength of the magnets, the distance between them, and the size and shape of the shield. A little experimentation quickly gets the correct result.
Shielding attraction between 2 magnets requires that each magnet have its own shield. The shield does not need to be in contact with its respective magnet, but it must be held fixed in position relative to its magnet. Again, the proper number of layers will depend on the strength of the magnets, the distance between them, and the size and shape of the shield. Simply add one layer at a time until the two magnets drop away from eachother.
Finally, a word about shielding just one pole of a magnet:
While this is not technically possible, it is possible to distort the magnetic field lines around one pole of a magnet. Remember to think about the magnetic field lines as travelling through the shield more easily than through air. Therefore, the shield acts as a “conduit” for some of the magnetic field lines. They still must travel from the magnet’s N pole to its S pole… but the path they take is what can be manipulated. This means that if you “shield” one pole of a magnet, you are basically relocating the place where those magnetic field lines emerge into air. The effect is the same as if you bend the magnet itself into a different shape.