In some degree it is possible to learn by training, but you need to have some chord-capable instrument and be able to get known chords out of it. Try to compare C versus Cm, E versus Em, A versus Am etc. Pick the middle of the sound range, not too high and not too low. After some practicing it should be possible for you to tell them apart. Minor chords always sound way more sad and romantic for some reason.

You do not need to identify all individual notes for that, you also do not need to separate between same type of chords (C from C# for instance) that is much more difficult task.