This may be a severe infestation of scale. You can scrape off/remove scale with alcohol wipes or a Q-tip dipped in rubbing alcohol, and then clean the scale off with it. Try to avoid getting the alcohol on the rest of the leaf/stem/plant. You need to clean up the entire plant to stop the infestation. 

If you decide to use insecticides, be sure it is labeled for use on Cressula ovata/Jade plant for scale, so that it does not damage the plant. (Horticulture soap can damage the foliage of this plant.) Whenever using chemical controls, always follow the label directions. 

Here is more information on Cressula ovata:

http://www.ladybug.uconn.edu/FactSheets/jade-plants.php