COMBINE vinegar with jam in a small saucepan and set over medium-high. Boil, stirring occasionally, until mixture turns syrupy and reduces by half, about 10 min.
OIL grill. Sprinkle salmon with salt and season with fresh pepper. Barbecue, skin-side down, with lid open, until a knife tip inserted into the thickest part of fish and held for 10 sec feels warm, 15 to 17 min for every in. of thickness. Brush with vinegar mixture, then transfer to a platter.