You would normally create a collection of the pics addde to your device and then sync via LR Mobile to LR desktop. The photos remain on your desktop computer even if you delete them from your device.
ou would probably first need to copy the Nikon photos to a folder. There is often a DCIM folder for jpegs and you can reate sub-folders within it.
Thanks Jon. I will be travelling with only my tablet. I shoot in raw to one card (Nikon D610, dual SD cards) and jpg to the other. My intent is to view the jpg images on the tablet, then bring selected images from a folder into LR Mobile to tweak them. The raw images will be loaded into LR desktop when I get home and adjust them as I did the "samples" when I was travelling.
I know I should be using a laptop while travelling, but I don't have one. So LR Mobile is my go around plan.