How do I see uplink messages?

Hi. If you're using AWS IoT Core for LoRaWAN, then you would use destinations to trigger an AWS IoT Core rule, or to publish an MQTT message to the IoT Core broker (which may in turn trigger a rule).

This page is the overall best summary: https://docs.aws.amazon.com/iot-wireless/latest/developerguide/lorawan-destination-rules.html. As stated, the message is base64-encoded. You will usually use a Lambda function to decode that into a JSON payload for other services to process and store.