no idea on the plant, maybe a Hygrophila of some sort.
To prune stem plants, use a pr of scissors and take cuttings about 6 inches long. Cut the plant about 10mm below a leaf node (where the leaves come out of the stem). Remove the bottom set of leaves just above the area it was cut, and then plant it in the substrate. Try not to damage the bottom of the cutting or it will rot and the cutting might die.