To make the dressing, whisk the yogurt, lime juice, and honey in a small bowl until smooth (if you’re using creamed or semisolid honey, melt it in the microwave before whisking). Add a bit of salt and pepper; taste and adjust the seasoning.
Peel the jicama, being sure to get the thin layer of stringy flesh off as you go (it’s right below the tan skin). Cut the jicama into ¼-inch slices, then cut each slice into small cubes.
Stand the unpeeled apple on its end and cut it into ¼-inch slices, as you did with the jicama. Cut each slice into thin strips so that you end up with apple matchsticks.
Put the corn kernels, jicama, apple, walnuts, and tarragon into a medium bowl. Drizzle most of the dressing over the ingredients and toss gently. Add the remainder of the dressing if you’d like more. Spoon the salad onto individual plates and garnish with a few herb sprigs.