KJV stands for King James Version, while NKJV stands for New King James Version. The critical difference between the KJV and NKJ is that King James Version was written by the bishops of the church of England explicitly to support the Ecclesiology and doctrine of that church. American versions of the KJV are different. It seems that NKJV is different from KJV.
The language between the two is quite different, which can be confusing for someone who reads both. Many people believe that one or the other is more truthful. KJV was written entirely based on the omission of the Alexandrian Manuscripts.
The NKJV, on the other hand, contains most KJV followers who reject the Alexandrian Manuscripts Translation of the Alexandrian Manuscripts. The New King’s James Version was partially written to reflect a period when translating the text into private experiences can mean different things to different people.