Core and finely shred the cabbage. Measure out 2 cups of shredded cabbage.
Trim, core, and finely shave the fennel bulb.
Peel and core the apple, then cut into matchsticks.
Combine the cabbage, fennel, and apple in a large bowl.
Add the lemon juice and toss to coat.
Place the celery seeds in a small skillet over medium heat. Toast for about 30 seconds or until fragrant, then immediately transfer to a small bowl to cool.
In a medium bowl, whisk together the skyr, mayonnaise, vinegar, mustard, honey, salt, pepper, and toasted celery seeds.
Fold the dressing into the cabbage mixture, being careful not to break up the apples too much.
Fold in the pecans and chervil.
Serve the coleslaw right away, or refrigerate until ready to serve.