Is the acronym "O.K." generally pronounced as an iamb or a trochee? Or is it context-dependent?
This specific question can be answered by any dictionary. However, there is a more general question underlying it which may merit closer attention, and that is how pretty much all two-letter letter-pairs in English place the stress on the second letter not on the first.
- A.D., B.C.
- B.A., B.S., M.S.
- U.S., U.K.
- P.S., M.C., D.T., A.I., G.I., O.D.
This includes O.K. — at least when pronounced as initials. The only exception is when the initialism has been assimilated into a pronounced word, in which case the stress falls more naturally on the first syllable, as in a Let’s welcome Deejay Somebody or that’s an okay try.
I suppose it’s possible that it’s actually the attributive use there that triggers the stress regression more than it is thinking of those things as spelt-out words. That, I’m not sure of.