Query which standard Maya dockControl is visible

Maya stores the Channel Box / Attribute Editor/ Tool Settings (etc) dock labels and control names in a global mel string array called $gUIComponentDockControlArray. From that, you can query which one is currently visible (on top):

import pymel.core as pm
mayaDocks = pm.language.melGlobals["gUIComponentDockControlArray"]
for i in range(0, len(mayaDocks), 2):
    label = mayaDocks[i]
    ctrlName = mayaDocks[i+1]
    print label, ctrlName, pm.dockControl(ctrlName, query=True, r=True)

Which prints something like:

Channel Box / Layer Editor MayaWindow|dockControl1 True
Channel Box MayaWindow|dockControl2 False
Layer Editor MayaWindow|dockControl3 False
Attribute Editor MayaWindow|dockControl4 False
Tool Settings MayaWindow|dockControl5 False

Note that if they're floating, they'll return True.