The new growth points are where the leaf joins the stem so deciding how far to cut back depends more on where these leaf nodes, as they are called,occur. Each node will produce a new branch.

If I have a leggy plant, I would want to cut the plant back to the lowest node or 2. The issue though is that you will still not have a lot of branching other than possibly from other buried nodes.

In that case, I would let those new branches grow and use them for future cuttings for use when I can provide better lighting so that they grow more compact with less space between the leaves. After you cut, try to provide as much lighting as you can so that these new branches are not leggy as well.

You can also try rooting the parts you cut off for extra plants.

Finally, there may be nodes on the stem where old leaves have been removed or fallen off. These can still successfully produce new branches so depending on whether they are there or not might also affect where to cut and how much branching you will initially get.

Hope this helps.