CUSTOM SETTING MENU -> d Shooting/display -> d3 ISO display -> Show ISO sensitivity
When you activate the camera it will show the ISO, bottom right. You can press almost any button and it will still display ISO. But while you half-press the shutter release, the display will change to show shots remaining in the buffer, it will revert back to ISO when you release the shutter button.
If you use AF-ON, it will still show the ISO value while you press that. Only the half-press of the shutter button will change to shots remaining in the buffer.
Note that "shots remaining" are for the actual buffer, not the "200 continuous" remaining shots, which is attained because the buffer is written to the cards so fast
JC
Some cameras, some lenses, some computers