I am using Adobe Draw for the first time, I am pretty happy with my line work so far, but I am having an issue of where to put my highlights and shadows.
This is my attempt
This is the image without any shadows or highlights.
I'd say you haven't placed the shadows and highlights in the right place.
Imagine where the main light source should be, to work out where to place shadows and highlights.
For example, if you imagine the light source is above and to the left, the shadows and highlights will fall something like this. This is just a very rough sketch.