scarf is worn under or over the jacket?

Answer 1

For warmth I'd say under the jacket.

Answer 2

The practical use of a scarf is generally under the coat.  It is around the neck, and you tuck it under the coat so it doesn't catch on anything and accidentally strangle you. I personally am not a big fan of risking strangulation just to be warm.

As a fashion accoutrement, I suppose it is however you want it, but since it is an accessory, I would expect it to be visible, and thus outside the outerwear. However, you could deal with it much like a necktie and have it outside all but the coat or jacket.

Answer 3

Mostly Over the jacket. But you can wear and style it however you want