I have a healthy Wandering Jew (Tradescantia zebrina) that is growing fast, and I want to know the best way that I could propagate it.
Wandering Jews grow fast, and you have to rejuvenate them regularly, or you will get a long plant that is bare at the base. You usually propagate by cuttings, and use several cuttings per pot in order to make a fuller, more balanced plant.
Prepare the pot first. A six inch diameter pot will do. A huge pot will have drainage issues, and in a tiny pot, well, you'll just have to repot later. Fill the pot with regular, free-draining potting mix, the stuff the plant will permanently stay in.
Take the cuttings. I do this by finding a stem, pinching the tip at the first mature leaf node, then counting nodes downward on the stem. I take a branchless stem about 5-6 nodes long, and cut it below the last (6th) node. Remove the two bottom leaves, and insert those first two nodes into the prepared pot of mix. They will root from the nodes in the mix. They will show above-ground growth from the leaf bases. They should each put out 2-3 branches. Expect growth within 3 weeks.
Keep the mix slightly moist at all times, until you see top growth. Then switch to only watering when the top 1/2" of mix dries out. Fertilize lightly when the new growth grows out a couple inches. Keep fertilizing once every other week thereafter.
Every 4 nodes on each stem, pinch the tip off. This promotes full, bushy growth. When it's getting overgrown again, allow the ends to grow out, providing cutting material to restart the process.
Wandering Jews are awesome plants, and it's very easy to take cuttings of them (much as it's easy to take cuttings of spider plants, golden pothos plants, the houseplant version of creeping Charlie, etc.) As a teenager, I had a wandering Jew plant (it was all one color), and I would regularly take cuttings of it, rooting them in water (just take a piece about 4 to 6 inches long and sit it in a cup of water (with one or more of the intersections where leaves grow in the water) on the windowsill until it grows roots—which shouldn't take too long—and plant it in potting soil when it has enough roots). That was very easy to do with this plant, in my experience. I imagine it's even easier to root it in seed-starting mix (although you might want to repot it in potting soil after a while, since there isn't much nutrition in seed-starting mix).
I imagine what J. Musser says in his answer is correct. I just wanted to share my experience, too.