Dracaena marginatas thrive best in bright indirect light; a few hours of direct sunlight is OK. Placement directly in front of an east or west facing window is best.
Have you recently repotted the plant
? These plants
have small delicate root systems that make them particularly susceptible to root rot if overpotted as yours appears to be. Marginatas need to dry out quite a bit between waterings. Overpotting leads to soil staying moist too long leading to root rot which may be causing your symptoms. I suggest removing the plant
to examine the rootball for firm, healthy, whitish roots, trimming away any roots that are black, shrivelled, or mushy, then repotting the plant
in the smallest pot in which the rootball will fit. Then let soil dry out to a depth of about a quarter down the pot between waterings.
Marginatas will not regrow dropped leaves. If you don't like the sparse appearance of the plant
, you can cut it as far back as you wish without harming the plant
. New growth will emerge just below the cut. You can also try rooting the top 6-8" of the tip cutting by stripping the lower leaves and placing the cutting in damp rooting medium and tenting the pot to keep in moisture until the cutting roots. Place the tented pot in a warm, bright location. Lift the tenting occasionally to release condensation or to check soil moisture, however, it is unlikely the cutting will dry out before it roots, indicated by emerging new growth in about 6-8 weeks. Then remove the tenting gradually over a week.
Good luck with your Marginata!