Peel the kohlrabi, cut the fibrous ends off, then cut into cubes (as you would for a potato salad).
Place into a large pot, cover with boiling water, bring to a boil and boil until fork tender (15+ minutes depending on how much kohlrabi you have).
Rinse in cold water, add the egg, onion, spices, and mayo and toss to mix.
Cover with saran wrap and refrigerate until chilled.