Remove the stems from the kale and chop it into bite-sized pieces. Chop the lettuce into bite-sized pieces.
Peel the kohlrabi, beet, and carrots and chop them into matchsticks (julienne); take care when peeling the beet as the color can stain. Remove the sections from one half of the grapefruit and peel them.
In a medium bowl, whisk together 2 tablespoons grapefruit juice from the other half of the grapefruit, 1 tablespoon honey, 1 teaspoon Dijon mustard, 1/2 teaspoon kosher salt, and 1/4 teaspoon freshly ground pepper. Gradually whisk in the olive oil one tablespoon at a time until a creamy emulsion forms. Taste and add additional grapefruit juice as desired.
To serve, place vegetables on serving plates or in bowls. Top with grapefruit vinaigrette and pepitas.