I can think of some tricks for this. But I wonder why you are tracing over lines you already have modeled, can you explain your use a bit so that the answer will suit you? Why not use the lines you have or just delete the ones you don’t want to leave the ones you need?
EDIT: Apologies, I just noticed that you wrote imported jpeg. I was confused by you saying you had exploded the import which led me to believe that you were dealing with raw geometry. You should not necessarily need to explode the imported jpeg to trace over it.
One quick trick is to switch to a style that has colored edges. Or simply modify the current style to make edges a color. Here I edit the current style to set edges to red. A further trick is to turn on X ray mode View>FaceStyle>Xray, which will quickly make the jpeg semi transparent and make your new lines easier to distinguish.
Also assign your jpeg to a separate tag so you can toggle it on and off easily, this helps to check your progress and spot errors.
