The phrase:
It's about finding the city's DNA
is used in a CNN promo for its program "Quest´s Worlds of Wonder". I can see what they want to express, but does it make sense in terms of language use?
That is just a figurative expression, one that is quite common in English. What DNA means there is something akin to the essential nature of the item in question, what makes it unique or special.
Your CNN expression could be reduced as follows:
It's about finding the essential nature of the city.
