You might do better asking in the Photoshop Forum but I wouldn't use the Clone tool.....
You need to have your master photo and the one you're copyng from open at the same time in Photoshop.
I'd then select the bit I wanted to copy using the lasso tool with some feathering (how many pixels to set the feathering to depends a bit on the size of your photo and indeed the selection, start with a low number (<10). Copy the selected (Ctrl-C) then switch to the target photo and paste it where you want it to go. If the photos are exactly the same you might be able to do "Paste in Place" (Shift+Ctrl+V) but more probably you'll have to move the selection by hand until it's in the right place.