Does a gold field draw a resource and commodity, when combining Seafarers and C&K?
Your are correct. I believe that the official Cities and Kights rules are clear enough for this:


  Commodities are produced only by cities, and only in forest, pasture, and mountains.


It might be different if Cities always produce commodities in C&amp;K, but that's not that case. Cities on grain or brick don't produce commodities, and C&amp;K rules specifically mention which lands produce commodities. Gold should be treated more like grain and brick; you get double resources.

Here is a link to an answer on the German FAQ: http://www.siedeln.de/faq/327_152_de.html

Roughly translated, it says no you cannot take commodities from the gold field; and it explains it by saying that every rule still counts unless it is specifically countered by a different rule; so the Seafarers rule about what you can get from a Gold Field still applies; because the C&amp;K rules don't specify otherwise.