Jem thinks that Atticus has clinched the case by establishing that dwells is left-handed however scout is skeptical that the information proves anything. What are her doubts?

Scout does not understand exactly how this evidence clearly exonerates Tom Robinson. I think Scout understands that the jury has probably made up their mind about Tom's guilt before the trial even started.

Scout doesn't know how it will connect to Tom Robinson. Also, the jury will vote in favor of the Ewell's because they are white, they knew the results before they even started