According to the photographer, this specific image was made with an in-camera multiple exposure. They first photographed the person, then overlaid a second exposure of sparkling light particles—likely reflections on water—so the bright dots appear over the darker parts of the portrait.

A similar look can also be faked optically by putting something close to the lens, such as glass with water droplets on it. If those droplets catch light, they can turn into out-of-focus foreground highlights. Their shape depends on the lens aperture, focus, and distance from the lens.

So for this exact photo: multiple exposure. For a comparable effect: create bright foreground highlights near the lens and shoot them out of focus.