"在修辞学上" can be translated as "rhetorically" or "in terms of rhetoric".
"Rhetorically" is an adverb that directly relates to the study or use of rhetoric, indicating a manner or style of expression within the realm of rhetoric.
"In terms of rhetoric" is a more descriptive phrase that explicitly places the discussion or analysis within the context of rhetoric.
Both translations are accurate and can be used depending on the specific context and desired emphasis.