Glue the magnet pretty much anywhere on the cd*, with a pole facing radially outwards. If the magnet's pole does not face radially outward the compass will be decieving.
To find the poles, place the magnet in the presence of other magnetic objects. The magnets will attach to each other along their poles if they have enough mechanical freedom to.
- Depending on magnet size, glue-ing too far away from the cd's center will tip the cd (think center of mass). But, if the magnet is too close to the center the torque arm length about the center will not allow for the compass to spin / function properly.