Question: how far can neji see?
Answer: In part I, it is noted that Neji, Hinata, and all Hyuga's initially had a range of 50 meters. After training, Neji increased his to at least 800 meters, whereas, Hinata was able to 10 km. They can use the Byakugan as sort of an X-ray vision and see through walls and even some barriers.