With a prayer plant you want to get the node in and two leaves if possible. One leaf is ok, but you need the node. This is the wider knuckle where branches grow from. It is also where the cutting will root from. You can take multiple cuttings if you like.
I use filtered water as they can be sensitive to ‘hard’ water. A fairly thin jar is ideal as they hold the leaves out of the water but allow the nodes to be fully submerged. Leaves can rot if they fall in the water.