Mix the yogurt in a salad bowl with sugar and lemon juice and season the dressing with salt and pepper.
Peel the kohlrabi, wash the apples thoroughly, cut them into pieces and remove the core. Cut the kohlrabi and apples into large pieces, then grate them in fine strips in the bowl. Drain the mandarins and mix with the raisins and chopped nuts into the salad. Let it steep and season again before serving.