What is Copernicus referring to when he states that "circles have poles different [from the earth's]"
Remember that Copernicus was espousing a heliocentric Solar System.  What he means by "pole" is the object's axis of revolution and its axis of rotation.  The Earth rotates around its poles: i.e. the North and South pole.  A line between those poles is our axis of rotation.  The axis of revolution would be the axis about which the Earth orbits.  This would correspond to an imaginary line at the Sun. 
 Copernicus is presenting the idea that the axis of rotation is not the axis of revolution.