Peel the kohlrabi. Peel it vigorously and completely—the peel is quite tough and fibrous so don't err towards keeping any of it around.
Grate the kohlrabi on the large holes of a grater into a bowl (or use the grater attachment in a food processor).
Lift the grated kohlrabi out of the bowl and onto a double layer of clean kitchen towels or multiple layers of paper towels. Lift the corners of the towel(s), twist them together, and squeeze out as much liquid as you can. Seriously, squeeze hard—properly "drained" and pretty much dry-to-the-touch kohlrabi is the absolute key to ending up with tender fritters rather than leaden pancake-like flops.
Crack the egg into a large bowl and beat it thoroughly with a fork—you want no strands of white clinging to the fork when you lift it from the bowl. Combine the kohlrabi and the egg.
Sprinkle the mixture with the flour and salt and stir to combine thoroughly.
Heat a generous layer of oil (about 1/4-inch deep) in a large frying pan or pot over medium-high heat until the oil shimmers when you swirl the pan. A bit of batter dropped into the pan should sizzle immediately.
Put generous spoonfuls of batter into the pan and flatten the resulting mounds a bit with the back of the spoon. You should be able to fit about four fritters in a large pan at a time. Partially cover and cook until the fritters are browned on one side, 2 to 3 minutes, flip, partially cover again, and cook until they are tender and browned on both sides. Transfer the fritters to a paper towel-lined plate to drain. Repeat with remaining batter. Serve immediately.