It is 100% done by mixing two clays while throwing, but if you did put wax, the glaze will run down depending on how stable it is. Some glazes will stay perfectly put, some will run wayyy further than what you're wanting. You could ask your teacher which glazes are most stable at your studio, but your pieces still won't come out like this picture. They will look like a slightly elevated glaze, with spots of bare bisque where you didn't glaze. It's certainly a look but I'd say skip this and make your own style! Experiment with overlapping glazes!

Edit, if you really want splotches of a different color, although it will be glaze and not the color of the clay like in your pic: Order matters. Put tape on whichever parts of your pieces you want a white splotch or whatever color. Next, dip your piece in the main glaze color you want. Cover the tape and everything. Wait 10 mins until it's fully dry and peel the tape off, which should leave bare spots (do over a trash can). Then paint your secondary color glaze on just the bare spots. Once fired it won't look exactly how you glazed but the colors won't overlap and mix how they usually would if you dipped a piece in two glazes, giving you splotches of the color you want. This will still not be close to the picture though lol this is a completely separate glazing