I am using the wah guitar pedal during this song to give it the desired effect. I am also using a down, down & up strumming pattern for the rhythm guitar part which is consistent throughout the song. The guitar riff is use’s the Gm pentatonic scale and can be played using only your 1st and 3rd fingers. To really learn it, listen to the recording and play along.
The Wah effect pedal can be used for the rhythm guitar part Bob Marley is playing by pressing all the way down on your wah pedal. Using the clean channel of your guitar amp this should give your guitar more top end (treble).
The wah pedal can also be used during the lead guitar part that Peter Tosh is playing. You want to slowly press down on the pedal as you play the chord on the downbeat.
With guitar effect pedals less is always more, so try to be economic with your use of the Wah pedal when playing