EFM32ZGUSB - Connection Guide
The EFM32ZGUSB board has three connectors. The first is the USB connector. It accepts a MINI-B format plug.
The second connector is a 6 pin DF11 header that is used by the factory to load the initial bootloader. It is also useful for debug purposes. For example, it can be used for debugging with https://www.engimusing.com/collections/breadboard-aids-connectors-wiring/products/rstsw-1. The SWO pin can be used as a general purpose I/O pin also. Its Arduino pin number is 9.
The third connector is the 10 pin DF11 receptacle used for connecting various types of I/O to the microcontroller.
The Arduino Pin Numbers are what you will use in a sketch to control each connector pin.