In the Blade Runner, Joi is a hologram controlled by AI - this means that Joi's body is actually located inside the electronic chips in whatever device generates the light - like the projector located in K's apartment or in the billboards. In the movie we can also multiple times see that Joi is incorporeal - she can easily exist in the same place as physical objects (i.e. the hooker that K sleeps with, has her physical body replaced by Joi's hologram). All good so far... until we look at the emanator: it is a portable projector that lets the user take his Joi for walkies. The problem lies in the fact that Joi is interactive: she seems to see the surroundings, but since Joi has no physical eyes, she should see only what the emanator sees. She shouldn't be able to peek behind the corner of the wall, because the emanator laying in the middle of the room cannot see behind the corner, or to really be nitpicking at the concept, she shouldn't be able to see anything when the emanator is in K's pocket. Yet in few moments in the movie we can see Joi acting like she was seeing with her eyes, looking at things that should be invisible for the emanator - i.e. Joi has been watching the DNA data through the microscope-like oculars together with K.
Was she just pretending? Her reactions at surrounding that she can see with her eyes seem genuine - i.e. she is very distressed when K is unconscious in the car after being shot down, even while the emanator is lying on the floor and she is projected outside of the stuck door.
I'm not looking for a "real science" explanation of how the emanator works - something hand waved like "it's nanotechnology" would be sufficient, as long as you can provide some proofs.