I'm assuming you are looking to understand the overall power consumption by the devices - as opposed to just that consumed by downstream PoE devices? If so, we don't currently have the ability to make that directly available - though it's something we're working on - no timescale available on anything currently though. Right now the best bet would be to use MT40 IoT sensors, which would provide a wealth of detail around consumption by the attached device(s) It would also allow you to remotely power it / them off and on as needed - just be careful not to disrupt the connectivity to the gateway itself!
https://meraki.cisco.com/en-uk/product/sensors/indoor-sensors/mt40/