You ask:
Kamboja is the last of the sixteen great nations mentioned in the
Visakha Sutta, Uposatha Vagga, Atthakanipata, Anguttaranikaya. Where
is
it?
According to Malalasekera's Dictionary of Pali Proper Names, it sounds
like it's in Afghanistan since it is thought to have been on the
shores of the Kabul river. It is near or next to Gandhaara and on a
caravan route.