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

My answer is actually to join the end of one piece to the centre of the another: in the shape of a T.

if they stick together strongly, the lower piece is magnetic as the metal is really close to the pole.

if they don't really stick together it's because magnetic field is really weak in the centre of a magnet so the top one is the magnet.