What are the places of the permanent magnet that have the greatest magnetic effect? What are they called?

They are called POLES.
There are two types of poles, as we know – these are Plus (+ or N, colored blue) and minus (- or S, colored red).
A fun and interesting fact about magnets; if you divide any magnet into halves or unequal parts, then the parts we receive will all exhibit standard magnetic properties and qualities! This is due to the fact that the magnet consists, as it were, of smaller magnets and, when separated, poles are formed again and again.
It is thanks to the poles that we can use magnets for our needs, in the broad sense of the word (electrical engineering, electric motors, etc.).