You have one magnet with a marked north and south pole and a one unmarked magnet. How will you find the poles of the unmarked magnet?

We can find the poles of unmarked magnet with the following method :

1. Take the marked magnet (with known north and south poles).
2. Bring its north pole near one end of the unmarked magnet.
3. If it attracts, that end of the unmarked magnet is its south pole.
4. If it repels, that end is its north pole.
5. Repeat the test with the other end of the unmarked magnet to confirm.

This method works because like poles repel and unlike poles attract each other.