Can you solve the MAGNET RIDDLE? ft YouTube CEO Susan Wojcicki

Smash the bars on the floor and see which one getting smashed makes the force between them weaker, or file off small bits of both bars and hold the opposite bar near the pieces, magnetic filings will just stick to non-magnetic iron but if the bar they stick to is magnetic the pieces will collect at the poles and follow field lines. Also using the string you could see if either of them aligns  with earth's magnetic field. If that office filing cabinet happens to have a hot plate you could try heating one of the bars to iron's curie point and see which one stops attracting the other after heating.