Can Botox fix this marionette/jowl dimple that appears when I talk & smile? (Photo)

I recommend fillers to soften the nasolabial folds themselves and also lift around the mouth and cheeks to build underlying anatomical support. In our practice we combine Sculptra with other fillers "layered" on top and lasers, skin tightening treatments such as Thermage, Fractora, and Renuvion (J Plasma), thread lifting, and peels to get the most conservative, natural look. I suggest seeing a facial sculpting expert for a formal consultation. Best, Dr. Emer

This line looks like something that would be improved by some strong lifting techniques. If placing both fingers on the corners of your jaw and pulling back gets rid of this line, then this is the case. The ways to do this would be with a surgical lift or a non-surgical option like thread lifting or facial filler lift.
There are some great techniques using Vycross Juvéderm fillers that are not as good as surgery but can give enough lift to get rid of a line like this. I think you would be talking about 4 to 6 mls with a good injector.
To know if Botox would be helpful stick out your bottom lip like a sad baby and notice if the corners of your mouth pull down more on that side. If they do, then Botox might help.