All the nanobots are probably capable of rudimentary vision. They may only have a few pixels of resolution, but networked together this would allow for a very high-resolution composite image to be generated. It wouldn't even necessarily have to have specific nanobots assigned to imaging duty, I suspect that any of them located at the exterior would do so, giving it a complex panoramic view.

All the nanobots are probably capable of rudimentary vision. They may only have a few pixels of resolution, but networked together this would allow for a very high-resolution composite image to be generated. It wouldn't even necessarily have to have specific nanobots assigned to imaging duty, I suspect that any of them located on the exterior surface would do so, giving the T-1000 a complex panoramic view.