As @DGO mentions have a look at the pins on the connector, the cellular are reverse of what the Wi-Fi are. Normally on the base of the antenna the frequency range is printed, with the Wi-Fi antenna also saying “Wi-Fi”.
The Cellular diversity antenna is “optional”, but I use that term loosely as it should be properly terminated and it would be decremental not to use it. It is an alternative receive path for the modem to receive the same signal as the main path but due to RF signals taking diverse paths (due to reflection etc.) and thus it can decrease the RF spectrum noise and improve the signal quality. Think of it as you having 2 ears, cover one and your ability to “hear” is decreased significantly. If you ever instal external antennas, make sure you place the antennas some distance (at least 1.5 m) apart and also vertically separate them a little.