I've wracked my ears and did my best putting together the chords to What's Happening Brother. I don't have the best ear in the world so I'm sure I've made a few mistakes in there, but this is the general gist.
A few interesting features I could see:
* Jamerson is really upending these chords with pedal tones and inversions that make his lines wonderfully melodic. You may want to create a chart for yourself that erases all chord information except for the bass notes, and try playing with each of them.
* The song appears to be in the key of Eb but as far as I can see, the chords never resolve to the tonic ("one" chord). That's a pretty sophisticated idea, it makes the song sound to my ears rather Romantic and European.
* Some 7th and 9th chords seem to be in use in this song, which is also fairly sophisticated for that kind of music at that point in time. They give the bass player more options to create a melodic line.
* A word on the notation I used: "-" means "minor", "7" means "dominant 7th chord", "maj7" means "major 7th chord", "+" means "augmented" indicating a sharp 5th, "sus4" means "suspending a perfect 4th instead of playing any 3rd at all", "maj9" means "major 9th chord" and in this case, "Ddim7" means "D half-diminished 7th chord" which is D-F-Ab-C.
* Some people know this already, but a common technique (some would call it necessary) for g-tar players is to not voice the root of the chord when they play it. That way you need both the bass and the guitar in order to hear the whole chord. That may cause some confusion as to what chord you're actually hearing (it sure did for me), and it may cause you to hear the chords different from what I have written here. That's fine, like I said, I don't pretend to be an expert at this.
* Have fun.
A- x 8
Bb-7 x 8
Ddim7 | Ab+/G Ab/G | C-9 | C-9 |
F7sus4 | F7 | F-7 | Bb7 |
Bb-7 | Eb7/G | Abmaj7 | Abmaj7 |
F7sus4 | F7 | F-7 | Bb7 |
Abmaj7/Bb x 4
Abmaj7/Bb Ab-7 | G-7 | C-7 |
F-7 | F-7 | Bb7 | Bb7 |
Abmaj7/Bb x 4
Abmaj7/Bb Ab-7 | G-7 | C-7 |
F-7 | F-7 | Bb7 | Bb7 |
Abmaj9 x 10
Ab-9 x 4
finish on Ab-9