In Spanish, PO-ke-mon or Po-ke-MON, depending on which other words are stressed in the sentence and on whether the title of the game is translated. For example, Po-ke-MON Es-car-LA-ta, but PO-ke-mon HEART-GOLD.
In English, always stressed on the first syllable, POH-ke-mon.
I swear this would be easier if I still had my phonetic alphabet keyboard installed...