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

I can think of 3 solutions:
1) Use the file to file some fine iron dust (from bar #1). Magnetic dust will clump together, non magnetic dust will act like dust. If that doesn't work (let's say filing caused the metal to heat and lose it's magnetic properties) you can sprinkle the dust near the bars, the magnetic bar will push the dust into the magnetic field lines (maybe shake the working surface a little by tapping it with the mallet). This is by far the easiest solution.
2) Suspend the bars from a string and let them naturally come to a rest. assuming the 2 bars are far away from each other, one of them will orient itself towards the magnetic north. As someone who tried to improvise compasses before - this one is extremely tricky, and might take many attempts to get right.
3) Assuming the mallet / the file are made of non-magnetic metal (and not ceramic / rubber etc.) - you can suspend one of the bars on a string and twist it a few hundred times. Then place the mallet near the bar and let go of the string. A spinning magnet will induce an electric current through metallic objects the bar will come to a rest slightly faster if it is magnetized. We might also see a slight heating due to the electric current. This solution is a theoretical one,  I highly doubt it will create any noticeable difference (especially without any precise measuring device).