Peel the kohlrabi, cutting away the tough outer layer until the flesh looks pale and even. Grate it on the large holes of a box grater, then toss with 1/2 tsp of the salt in a colander set over a bowl. Let it sit for 15 minutes.
While the kohlrabi sits, stir the Greek yogurt, lemon juice, lemon zest, dill and a pinch of salt together in a small bowl. Cover and chill until serving.
Wring the kohlrabi in a thin clean tea towel, a handful at a time, until only a few drops come out. You should have about 500 g left. Mix it in a large bowl with the eggs, flour, Parmesan, scallions, garlic, baking powder, pepper and the remaining 1/4 tsp salt, until the shreds are coated and clump when pressed.
Heat the oven to 95 C / 200 F and set a wire rack in a 33 x 46 cm / 13 x 18-inch sheet pan. Heat a 30 cm / 12-inch nonstick skillet over medium heat for 2 minutes, then add 2 tsp of the olive oil.
Scoop four 1/4-cup mounds into the skillet and press each to about 1.5 cm / 1/2 inch thick. Cook for 3 to 4 minutes per side, flipping once, until deep golden and the center feels set. Move to the rack in the oven, then repeat twice more with the remaining oil and batter, wiping out any loose shreds between batches.
Serve the fritters hot, three per person, with the lemon yogurt dip.