In a small bowl, combine 1 Tbs. each of the oil and sambuca with the garlic, rosemary, fennel seeds, coriander, 1-1/2 Tbs. salt, and 3/4 tsp. pepper to make a paste; set aside.
Pat the roast dry with paper towels. Rub the paste over the entire roast. Cover and refrigerate overnight.
Position a rack in the center of the oven and heat the oven to 400°F.
Arrange the potatoes, parsnips, onions, and fennel in a 13x17-inch (or similar) roasting pan, season with 1/2 tsp. salt and 1/8 tsp. pepper, and drizzle with the remaining 1/4 cup olive oil. Roast, turning occasionally, until a fork inserted in the center of each type of vegetable meets little resistance, about 40 minutes.
Meanwhile, remove the roast from the refrigerator and let sit at room temperature for 30 minutes.
Reduce the oven temperature to 300°F. Put the roast, fat side up, on top of the vegetables. Add the chicken broth and wine, and roast, basting the meat and vegetables occasionally, until an instant-read thermometer inserted into the roast registers 135°F to 140°F, about 2 hours.
Transfer the roast to a serving platter or carving board, cover loosely with foil, and let rest for 20 to 30 minutes. With a slotted spoon, transfer the vegetables to a large sheet of foil; wrap and keep warm in the turned-off oven.
Pour the juice from the roasting pan into a fat separator and let sit until the fat rises to the top. Pour the clear juice into a 1-quart saucepan, leaving the fat behind, and put over medium-high heat. Add the remaining 1 Tbs. sambuca and simmer until the jus is slightly reduced, 3 to 5 minutes. Strain through a fine sieve and season to taste with salt and pepper.
Arrange the pork on a platter with the vegetables, garnish with the fennel fronds, and serve with the jus on the side.