I understand the concept of native ISO, and prefer to shoot the closest possible to my camera's native ISO. However, from my understanding, a given camera's native ISO can vary between 100 and 200, not eliminating the possibility that some have it outside that range.

Recently, I've been using a Nikon D3100, and would like to be able to shoot as close as possible to my native ISO. However, since I do use multiple different cameras (including the 6D Mark II, SD14, D7100, Rebel, and a couple others), this question should really be broader than just the D3100: How can I find the native ISO for a given camera, particularly Nikons?