detect powernap from the command line
You will not be able to connect to your Mac without waking it up. Modern Macs can be accessed remotely without needing to power on the display; this behaviour saves energy but is not Power Nap.

Apple's Power Nap technical note describes what the state is and how it affects your Mac.

Power Nap does not leave your Mac in a generally usable state; only specifically designed processes are permitted during the power nap state. The permitted processes do not currently include remote connections via secure shell (ssh).