Toast coriander seeds, fennel seeds, cloves, cardamom pod, and star anise in a small skillet over medium-low heat until fragrant, 5 to 7 minutes. Place spices in the center of an 8-inch square piece of cheesecloth; gather edges and tie sachet with twine to secure.

Cook 1/2 onion and ginger in the same skillet until lightly charred, about 3 minutes per side.

Combine 8 cups water, turkey carcass, sachet, charred 1/2 onion, and charred ginger in a large pot over medium-high heat; bring to a boil. Reduce heat to a simmer; simmer for 2 hours.

Fill a separate large pot with lightly salted water and bring to a rolling boil over high heat; stir in rice noodles and return to a boil. Cook noodles, uncovered, stirring occasionally, until noodles are cooked through yet firm to the bite, 4 to 5 minutes. Drain well in a colander set in the sink.

Remove and discard carcass, sachet, onion, and ginger from soup. Strain soup into a pot to remove any meat that may have fallen off the bones. Season soup with fish sauce and salt.

Divide rice noodles and 1 cup shredded turkey meat among 4 large bowls; scatter 1/4 cup sliced onion, basil, and cilantro on top. Ladle soup into bowls. Serve with a lime wedge and hot sauce.