Harmonics are always above the fundamental in frequency… and usually lower than the fundamental in volume. Sometimes the 2nd harmonic is louder… and om which octave you consider the fundamental is arguable and depends on context.
For chords it is always going to take some sleuthing because the very nature of a chord is that the harmonics of the root align with some of the fundamental and harmonics of the other notes. Timbres that have many harmonics, or effects like distortion will only make all of this fuzzier.
Analyzing the notes of a chord from a recording is still a tricky business. Even using latest machine learning, the results are only a starting point for transcription.
You can play with Magenta’s machine learning polyphonic transcription, tuned for piano for free, on the web without installing anything: https://piano-scribe.glitch.me/