I identify them from their accents. For example in Germany I can identify someone from Gujranwala, Gujrat, Sialkot etc. from his accent and the choice of vocabulary while speaking Punjabi language. I can even differentiate between someone from Gujranwala and someone from our neighboring Gujrat because people of Gujrat have some specific pronunciations of specific words different from us in Gujranwala. That is the level of accuracy in my case.
I can instantly identify an indian punjabi from the his accent and his vocabulary unless he happens to be from some migrant origin punjabi pakistani family. I have an accent and vocabulary detector ON all the time. I am basically a quasi linguist because I have been curious about various accents and preferred vocabularies of people since my teenage.
Edit: I just saw the OP and I noticed that he was "judging" various ethnicities, for me this is plain BS, every individual is different, I didn't like his stereotyping of the people. Great Gama the strongest man of South Asia was produced in central Punjab, not in Balochistan or KPK. There are tough punjabi, weak punjabi, tough pashtuns, weak pashtuns etc. There is no one size fit to all for all individuals of any ethnicity. After living in Germany and having interacted with multiple people from almost all major countries of the world I have stopped stereotyping the whole ethnicites because it is BS. The only exception to this rule are gangus of india.