Tim Hardwick, MacRumors:
Swipe left or right across the clickpad to scrub backward or forward in time. For more granular control, rest your finger on the outer edge of the clickpad ring until a ring icon appears on-screen, then trace a circle with your finger around the clickpad ring in a clockwise or counterclockwise direction.
Scrubbing has two modes. As Tim points out, scrub left and right on the clickpad works intuitively, scrubbing a paused video left and right.
But if you touch the outer ring first, a ring icon will appear, that’s your sign you are in jog mode and you can trace a circle to jog forward or back. Definitely a hidden, low-discoverability feature, but one worth knowing about.