Answer:
Finding the latitude and longitude of Mexico city is very simple. You only have too find the nearest latitude marker, which is 20 degrees North, and the nearest longitude marker, which is 100 degrees West. From there, in any sufficiently large physical map, or more commonly, in a visual map software, the more specific coordinates can be found.
In the case of Mexico city, the exact latitude is 19.4 degrees North, and the exact longitude is 99.1 degrees West.