Answer: The sweet potato is a heat and sun loving plant, it also needs a rich and evenly moist yet well drained soil, meaning not sopping wet or saturated, to do its best. For a container plant it is best to use a commercially formulated potting mix formulated for container plants rather than garden soil.
I would suggest you check with your local county extension to get a diagnosis of what is happening. It could be a matter of the soil being too cold, overwatering causing oedema (the bumps), lack of strong direct light, or a combination of problems.
While it is possible to start new plants using tip cuttings rooted in water, I would make sure the plant is healthy before propagating it. The cutting should be long enough to have several nodes, remove all but the top leaf and submerge the stem in water. Keep it in a warm sunny window until well rooted, then plant into clean soilless potting mix formulated for houseplants.
Good luck with your plant.
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