Heat the chicken broth in a medium saucepan over medium-high heat until very hot. Add the corn and cook until the kernels are just tender, 3 to 4 minutes. Transfer the corn to a cutting board and reduce the heat to keep the broth hot but not simmering.
Once the corn is cool enough to handle, slice the kernels off four of the pieces. Grate the kernels from the remaining two pieces using the large holes of a box grater. Discard the cobs.
Heat the olive oil and garlic in a large, heavy saucepan or medium Dutch oven over medium-high heat until the garlic is fragrant, about 2 minutes. Add the arugula and toss with tongs until wilted, about 1 minute. Season with a generous pinch of salt and pepper. Transfer the arugula to a cutting board, let it cool slightly, and then coarsely chop it. Wipe the pan clean.
Melt the butter in the cleaned pan over medium heat. Add the leek and a generous pinch of salt and cook, stirring occasionally, until softened, about 2 minutes. Add the sausage, breaking it apart with a fork or spoon into crumbles, and cook until no longer pink, 2 to 3 minutes. Add the rice and stir until the grains are well coated with fat and the edges become translucent, 1 to 2 minutes. Pour in the wine and stir until it’s absorbed, about 30 seconds. Stir in the grated corn.
Ladle enough of the hot broth into the pan to barely cover the rice, about 1-1/2 cups. Bring to a boil and then adjust the heat to maintain a lively simmer. Cook, stirring frequently, until the broth is mostly absorbed, 2 to 3 minutes. Continue adding broth in 1/2-cup increments, stirring occasionally and letting each addition be absorbed before adding the next.
After about 20 minutes, the rice should be just cooked but still fairly firm. At this point, add the whole corn kernels, chopped arugula, and another 1/2 cup broth. Continue to simmer and stir until the corn is warmed through and the rice is just tender to the tooth, an additional 1 to 3 minutes. Stir in another splash of broth if the risotto seems too thick. Remove the pot from the heat and stir in the cheese. Season with salt and pepper to taste. Serve the risotto immediately with a sprinkling of cheese and parsley, if using.