The Wah guitar pedal can be used for the rhythm guitar part that Bob Marley plays by pressing your fott all the way down on your wah pedal.
By using the clean channel of your guitar amp, the neck pick up, and a strong right hand picking attack, it should give your guitar the desired reggae tone.
The wah guitar pedal can also be used for the lead guitar part that Peter Tosh is plays. Begin by slowly pressing down your foot on the pedal as you play the chord changes on the downbeat.
In reggae music guitar effect pedals are used sparingly, so try think of the phrase "less is more" when using the wah pedal.