وَمَا تِلْكَ بِيَمِينِكَ يَا مُوسَىٰ
And what is that in your right hand, Moses?
The question serves an attention-directing, dialogic and preparatory function rather than a need to discover the object. Analysis of rhetorical questioning should separate interrogative form from intended conversational effect.
Replacing it in a constructed exercise with a bare assertion, “there is a staff in your hand,” would remove that exchange. Do not assume literal ignorance on the speaker’s part, nor draw speculative theological conclusions from a purely rhetorical classification.