White spots on your Jade plant can be caused by excess salt in your tap water. If the water does have excess salt, the plant will expel the salt through the leaf pores. This will not harm your plant, but you may want to consider using filtered, rain, or distilled water if you want to avoid this spotting. You can wipe off the leaves with a damp cloth to get rid of the spots.
Powdery mildew can occur on your jade plant if it’s sitting in an area of low air circulation with cool temperatures but high humidity. You can identify mildew by the small white circular spots that occur on the broadest parts of the plant. It will start on the leaves, and in more advanced stages will become fluffy strings that spread across the plant. To treat, you can spray the plant with a mix of 1 tablespoon baking soda, ½ teaspoon liquid soap, and 1 gallon of water.
Scale, mealybugs, and spider mites occur frequently in indoor conditions. White spots on your jade could be pests. We suggest looking closely with a hand lens or trying to scrape the spot off to see if it could be a pest. If not killed early on, these small pests proliferate and spread into nooks and crannies, making them more difficult to reach. The piercing mouths of the insects suck the energy from your plant, especially if your jade is already unhealthy from poor lighting, a nutrient deficiency or improper soil moisture.