Dembow — the one-bar drum cell under almost all reggaeton, lifted from Shabba Ranks' 1990 "Dem Bow" riddim (Bobby Digital / Steely & Clevie) and looped ever since. The kick is four on the floor; the snare plays "a of 1, and of 2" and again "a of 3, and of 4" — a 3-3-2 in sixteenths, i.e. a tresillo twice per bar. The composite "boom-ch-boom-chick" is the pattern's key, shown on the clave line.
The keyboard stabs copy the snare (short on the "a", longer on the "and"), the bass stays on roots with a push on the "and" of 2, and the hat ticks straight eighths. Two chords per bar — the familiar minor i-VI-III-VII loop — keep the harmony as static as the drums.
Listen for the snare's two positions: the first is a sixteenth before the beat, the second an eighth after it; that lopsided pair is the whole swagger. Practice: clap the tresillo (1, "and" of 2, 4) and notice that the dembow snare is the same cell started one sixteenth late. Compare reggae-one-drop — same island family, opposite relationship to beat 1.