All peripheral are visible in the Peripherals window. When you select a peripheral, you will then see its registers. See the Peripheral section of the User Guide.
Hope you are doing well.
Are you referring to the MCUXpresso IDE? If so what version are you using?
Could you please describe what you mean by the NVIC window so I can help you locate it, it is possible that you might have clicked on close view, but are able to reset it.
If you go to Window -> Show View it will show you the most common windows used. However if you click on others it will open several folders with different specific windows. Here you can browse through each folder until you find the one you need.