Polyscias scutellaria 'Fabian' is a type of aralia. Leaf drop on indoor plants is a normal reaction to the stressful conditions they experience inside - lower light intensity, lower humidity, short day length, and possible insect pests. We do not know how you are caring for the plant for example, watering, does it have holes for good drainage, humidity levels, etc.  

Your photos are out of focus. However, it looks like cast skins of spider mites, a sucking insect on the undersides of the foliage. They suck chlorophyll from the leaves. Symptoms of spider mites include leaf drop, yellowing, browning, webbing, etc.

You did not mention if the plant was outside during the summer or did you have other plants that were outside and brought indoors. You should isolate the plant from your other houseplants until the issue is under control.

At this point, you want to get the mite population down and focus on proper care. Periodically wash down the plant with a strong spray of water and get good coverage of the lower leaf surfaces. Any eggs will cycle through their life cycle. You can pick off heavily symptomatic leaves only to get ahead of this.

If new foliage has symptoms, you can use insecticidal soap to reduce the mite population. Follow label directions and make sure the plant and pest is listed on the label.  Here is our page on spider mites https://extension.umd.edu/hgic/topics/spider-mites-indoor-plants

These plants like bright light without direct sunlight. Do not subject the plants to temperatures below 65 degrees. Increase the humidity by growing on trays of moist pebbles. Water moderately throughout the year moistening the potting mixture well at each watering but allowing the top half inch of the mixture to dry out before watering again. Make sure the container has holes for good drainage. Apply standard liquid fertilizer every two weeks from early spring to late fall only. They grow slowly during the winter. 

Also, here is a link for more information  https://www.ukhouseplants.com/plants/polyscias-dinner-plate-aralia

Marian

Ok let me add some details to be sure. We keep the Fabian indoors, always. It sits near a northeast facing window. We keep the house between 69-70 degrees. It is in a pot with holes at the bottom and a saucer. We recently added peat moss to the soil, as well as pearlite. My husband was watering it 2 cups of water about once a week.  

At one point it was sitting near an air vent. And we thought maybe the draft was causing the leaf drop so we moved it however it has not recovered in fact it seems to have gotten worse. It was only leave dropping on one stall but now several stalls are having yellowing dots. Some leaves are so fragile that if I barely touch them - they fall.

Let me try to re add the photos because on my end they look clear. One is the top of the leaf close up showing the yellowing and one picture is the back where I noticed white “dust”. 

With regards to watering, it would be best to monitor the plant regularly but water only when needed, rather than on a schedule. (We realize your two-week interval may be how often it was needing water and perhaps not a timed schedule.) Two cups of water for this size of pot may or may not be enough...it's difficult to judge from description alone. Instead, what would be best is to water it over a sink (or a sufficiently deep saucer/container if too heavy to carry to the sink) to the point where the excess water is freely dripping out of the bottom drain holes. That way, you know that the entire soil depth has received sufficient wetting, and the excess water can also carry with it some of the minerals and fertilizer residue, which will lessen the speed of buildup that will necessitate repotting to alleviate in the future. When plants are watered an amount that doesn't drain out of the bottom, it runs the risk of over-watering the shallower roots and under-watering the deeper roots. Spider mites in particular tend to thrive on plants that are stressed due to moisture issues - both soil-borne and atmospheric humidity.

A humidity tray may help raise the humidity levels around just this plant, and might suffice if the air circulation in this location isn't very high. Otherwise, a room humidifier (or perhaps one of the smaller mini "personal" humidifiers) would be more effective, albeit a larger investment. A range recommended for human health and comfort - 40 to 60% - will also benefit indoor plants.

Peat moss is a common ingredient in bagged potting mixes, though it can be challenging to work with in some circumstances as it tends to not readily absorb water when it's become fairly dry. As one ingredient of several, though, it's usually not very detrimental. Perlite is a good choice for improving drainage, and while almost all bagged potting mixes include it, some seem to be lacking in sufficient drainage unless additional perlite is added. When the plant next needs repotting, it will be best to remove as much of its soil as possible and replace with fresh, regardless of what additional components you wish to add to a bagged mix (or you can also mix your own). There are dozens of potting mix recipes and recommendations in books, blogs, etc., but each has its advantages and disadvantages that will also vary with the grower themselves and the environment they provide for the plants. Essentially, as long as the plant's roots get the oxygen and moisture they need, a gardener can tailor their care to get most ingredients to work for them. Because unintentional over-watering of potted plants is a common occurrence, using more perlite for improved drainage is a safe bet.

The photo of the leaf underside does appear to show a spider mite infestation, and they do happen to thrive in drier environments. Raising the humidity, regular leaf rinsing (especially the undersides), and perhaps a round of treatments with a pesticide labeled for indoor use like the aforementioned insecticidal soap will all help to knock-back this population and keep them under control; they may even eliminate them. When using a pesticide, make sure to follow the label directions regarding dilution rate (if needed) and how often to re-treat, as multiple applications will be required to catch all of the pest's generations; overly-frequent applications may damage plant tissues.

Looking forward, if you have the option, the plant would benefit from spending the summer outdoors due to the higher light levels, good air circulation, and high humidity; the benefits of greater vigor and the renewed energy reserves it accumulates will help it to tolerate overwintering indoors. If you do this, it should be sited in a mostly shady exposure, and can be occasionally fertilized as Marian mentions to promote good growth. As for timing, the window from about late May to early October should be fine. It can then be inspected (and treated, if needed) for any hitch-hiking pests before being brought inside. If you need or want to keep it inside permanently, that's fine, but give it as much light as you can in the growing season so it can photosynthesize well and minimize stretching for light. Insufficient light can be one trigger for premature leaf loss, though there are other, often overlapping stressors that can also cause it. (The light recommendations between indoors and outdoors may seem contradictory, but outdoor shade light levels are actually as-bright or brighter than indoor sun light levels; our eyes adjust too easily to make them a good detector of actual light intensity.)

Miri