I hope to find the name of this plant and the reason why it is dropping its leaves ..
This plant must be 15 years old. It seems to be losing leaves….the bottom stock/leaves fall off then the next one, then the next one, etc. it appears healthy but what can I do with the long bare stock? I have it braced up so it won't fall over. I'm afraid of losing it. I water it from the hole in the plant pot and not from the top. All of my other plants are quite healthy. Thank you in advance!

You plant is weak, slim, floppy and not standing up strong because you are not giving it enough light!
Put it directly in front of the brightest window you have. Not across the room from a window.

Agree. It would be more sturdy with more light.

It look like a Schefflera. Not sure which species.

As the trunk lignifies (turns woody), it's normal for the older leaves to fall off. This can seem overly dramatic for a Schefflera because the leaves are compound so it seems like a lot of leaves are falling when one leaf falls. The compound leaf has about 7 leaflets and a long petiole, which are a single leaf.

Schefflera arboricola (Dwarf Schefflera)