Make the gnudi: Place ricotta in a sieve lined with cheesecloth, and set over a bowl. Refrigerate at least 2 hours (or overnight) to drain. Discard liquid.
Combine ricotta, Grana Padano, nutmeg, salt, and pepper.
Spread semolina flour on a rimmed baking sheet. Form 1 heaping teaspoon ricotta mixture into a ball. Gently roll in flour to coat, then nestle in the flour. (The flour will form a coating on the gnudi, helping them to keep their shape as they cook.) Repeat with remaining ricotta mixture. Cover with plastic wrap, and refrigerate overnight.
Make the roasted-corn sauce: Preheat grill to medium-high. (If you are using a charcoal grill, coals are ready when you can hold your hand 5 inches above grill for just 3 or 4 seconds.) Bend back husks of each ear of corn, remove silk, and replace husks. Grill corn, turning occasionally, until charred on all sides, about 15 minutes. Let cool. Remove husks. Cut kernels from cobs, reserving cobs for corn stock (recipe follows).
Cook salt pork in a skillet over medium heat until golden and barely crisp. Add corn kernels, scallions, and 3 cups corn stock, and bring to a boil. Reduce heat to medium-low. Stir in nutmeg and cayenne, and cook until slightly thickened, about 8 minutes. Stir in butter, salt, and black pepper. (If a thinner sauce is desired, add more stock as needed.)
Bring a large pot of water to a boil. Add 1 tablespoon salt. Cook gnudi in batches (do not overcrowd pot) for 1 minute. Using a slotted spoon, transfer gnudi to sauce, and toss to coat. Serve garnished with scallions, black pepper, and shaved Grana Padano.