The Flashforge Inventor II does not have an onboard ethernet port. From the factory, your only option is to use WiFi.
If you're a school that prefers to use Ethernet, you can purchase a USB to Ethernet adapter like the one seen below. This plugs into the USB port on the right side of the inventor. The adapter only works if you're on the latest firmware, found here. The UGREEN adapter shown below is the one we support and recommend.