Do you have just the frame, or a complete bike? If you have only the frame, measure the width of the bottom bracket shell. If it is 68mm, it is most likely English threading. Look at the threading direction of the fixed cup side. If it is left hand threaded, it is also likely English. Could be Swiss, but I doubt it.

If you have a complete bike, just remove the crank; the threading type may be engraved on the fixed cup.