----- Original Message -----
You're trying to figure out what the power notification is, or something else? You haven't actually presented a question :)
The power notification is, I believe, "Your system is going to get suspend soon due to inactivity" (or phrased similarly). Once you touch an input device, the notification gets destroyed. The presentation is somewhat confusing, I agree. For verification, disable screen blanking. You should see the same power notification pop up some time before the 15 minutes suspend timeout.
It probably doesn't make sense to show this particular notification on the lock screen (instead the lock screen could show something like "suspending in X minutes" somewhere visibly by itself). But the sender of the notification can't probably enable/disable lock screen visibility on a per-message basis (but I haven't looked at all the available hints you can attach).
The notification should be visible, as it should wake the screen up when it appears, and also be visible when other notifications appear (which should also wake up the screen).
It should be gnome-shell making the decisions of whether to wake the screen up or not, not the caller (see the WakeUpScreen D-Bus signal in both source trees for details).