Its the connection for the pitot sensor that is used to measure speed. You only need one. The pitot sensor measures the water pressure on the forward edge of the lower unit. If you look closely you will see a small hole. That often gets plugged. the sensot has no parts per se, it jut routs water to a sensor on the motor or in some cases actually sends water pressure to the speedometer itself. There should be a small diameter hose that connects to the fitting you see and runs up into the motor where it connects to an electrical sensor.
If the pitot is not plugged (how do you know? The dash spedo gauge does not display accurate or ant speed info) and the tube is not connected, sea water will spurt out into the pump housing area. . The fitting should be plugged if not connected to the tube
