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human
[Star Wars] If Darth Vader was to use Force Lightning, would it come from his arm stub or his artificial fingertips?

Palpatine's and Dooku's Lightning comes from their extremities, and since Vader's extremities are his stubs, it would make sense that the lightning would come from there.
gpt
It'll come from Vader's hands as well.  The Force doesn't so much care whether your hand is biological or not as it does whether or not you consider your hand a part of yourself.  
Given that Vader uses hand gestures as part of how he uses his other Force powers, they're likely to be involved in Lightning.