Cacao percentages and aromas developed in chocolate from different origins
The cocoa plants/grains were grown in different areas, the soil they grow in will have different mineral content; the heat and humidity will be different, the plant will grow in different ways resulting in cocoa pods and grains will be different.

They will have different flavors, sometime it is subtle, sometimes it is obvious.

This is what people, in mostly wine countries, call terroir.

The only way to train yourself tasting chocolate is to taste more and more chocolate and taking notes. 

The most difficult thing when tasting is to find the proper words; sometime you will taste of smell something subtle, but you cannot make the connection with the actual corresponding word.

You will smell something that smell like nutmeg, but your brain is not trained enough to make the connection.

You can find Wine Aroma kits containing small vials of "flavors" that you can use to train your nose. This can be used even for chocolate, just as a training tool.

(Anecdotal) I'm part of a wine tasting group, most of the other attendants are translators, writers, and they are better than I am in finding words corresponding to what they smell and taste.