Instead of a knob there is a little lip that you can grab with your index finger.
To further befuddle or amuse me, I've also noticed that if they DO have a knob it's placed dead center in the door and they don't attach to any mechanism and there is no standard height and no leverage.
So, if you are trying to enter through a door with a centered knob you basically just have to thrust your body at the door. Why?
I googled "door knob in center of door", to see if there is some reason way back in history that has just carried forth. All I found were other googlers wondering the same thing. I think they are purely decorative.
What do you think?
Centered knob (very high mount)
No knob (incredibly low mail slot)
Just barely qualifies as a knob