Which section at Chaengwattana should I go to for transferring an Extension to a new passport?

The section for transferring an Extension to a new passport at Chaengwattana is the same section where you originally obtained your extension. If your extension was issued in section N, you will need to return there for the transfer. If you're concerned about timing, it may be better to wait until November 8th when you plan to renew your annual Extension, as you may be able to manage both the transfer and renewals in one visit.