The skank — reggae's off-beat chop, played by guitar and keyboard together. Nothing on the beat: a short chord on the and of every beat, here with the "double skank" Scivales writes on the first and third of them (two sixteenths, the second accented, and-a) and a slightly longer chord on the and-of-2 and and-of-4. Scivales writes it at 160 with chords on 2 and 4; at half speed, 80 bpm, the same hits fall on every "and", the way reggae is usually counted.
How it sits: the drums play one drop (kick and snare together on 3, nothing on 1), so the skank's off-beats and the bass are what tell you where the beat is. The bass line is standard practice — roots that start on 1, a pickup on the and-of-2 and a short walk up to the next bar; the percussion layer is quarters.
Listen for how empty the downbeat is: piano and guitar never touch it. Guitar chops are downstrokes with the "a" sixteenth as an upstroke; damp immediately.
Practice: metronome on quarters, play only the "ands", and keep the chords shorter than you think.