For the labne: Line a sieve with cheesecloth. Mix together the yogurt and salt, and spoon into the cheesecloth. Wrap the edges of the cloth over the top of the yogurt, and place the sieve over a large bowl to collect all the whey that drips off. Place your contraption in the fridge and let it drain overnight. What's left on the top of the cheesecloth is labne!
For the vinaigrette: Use a sharp knife to separate the skin of the preserved lemon from the flesh. Discard the flesh. Cut the skin into a julienne, and then into a small 1/8-inch dice. Mix together the preserved lemon, olive oil, lemon juice and a small pinch of salt. Pit the green olives; I use a cherry pitter, which makes an easy and fun job out of it. Cut each olive in half lengthwise, then give them a rough chop. Mix into the vinaigrette.
Gently toss the greens into the vinaigrette. Spoon a few dollops of labne onto a plate or platter; top with the kohlrabi, a spoonful or two of the preserved lemon vinaigrette, a scattering of greens and olives, a few cracks of black pepper, and a pinch of sea salt. Repeat this once more, layering greens, kohlrabi, labne, pepper and sea salt.
Labne is yogurt cheese. You can buy it, or you can make your own using the recipe included.