If you place the north pole of a bar magnet near an unmarked magnet and they repel, you can conclude that the unmarked magnet's pole facing the bar magnet is also a north pole.

Here's why:

* Like poles repel: Magnets have two poles, north and south. Like poles (north-north or south-south) always repel each other.

* Opposite poles attract: Opposite poles (north-south) always attract each other.

Since the north pole of your bar magnet is being repelled, the unmarked magnet must have a north pole facing it to cause this repulsion.