Questions about example sentences with, and the definition and usage of "Memon"

In the original sentence, you said "Karachi city" to show that it is Karachi and Karachi is a city. However, it is not grammatically correct to simply say "Karachi city." You can say "Karachi City" with the capital "C" if that is the official name of the place (for example, Mexico City or New York City). Otherwise, you have to say "city of Karachi." Actually, you don't need "of" and if you say "city Karachi," it is still fine. However, "city of Karachi" sounds better and you will see people use it more often.