How to pronounce Mahon?

(Ma-Hone)

Last name

Irish

Son of the bear

This name is of Irish origin, pronounced Marn, as in barn...

ma-hon

Almost like the first two syllables in "mayonnaise," except that the "a" is between long and short.
In Ireland, the "a" is short, even though the first syllable is accented, and the "h" is often but not always pronounced.

Ireland

Happens also to be the capital of Menorca, where it is pronounced Ma-OHN (accented second syllable, long "o")