When evaluating a text for its argument, the most relevant question to consider is:
Is there enough evidence for the claim?
This question directly addresses the strength and validity of the argument being presented. Evaluating the quality and amount of evidence helps determine if the claims made are substantiated and reliable.
While the other questions mentioned (sources, narrative style, and grammar) can provide context and influence the overall effectiveness of the text, they are not as critical when focusing specifically on the evaluation of the argument itself.