B.G 11.31
ākhyāhi me ko bhavān ugrarūpo namo'stu te devavara prasīda। vijñātum icchāmi bhavantam ādyaṁ na hi prajānāmi tava pravṛttim ॥31॥
Declare to me — who are you, O fierce one? Salutations to you, O best of gods, be gracious. I wish to know you as the primordial being, for I do not indeed know your origin or nature.
Gīta Bhāshya 11.31
The question “Who are you?” in the context is asked to know various other aspects of the supreme being. It does not mean Arjuna is completely ignorant of the Lord's significance, as he is addressed as 'O Viṣṇu' (in verse 30).
dharmāntarajñānārtham eva "ko bhavān" iti pṛcchati। yathā kaścit kiñcit nāmādikaṁ jānann api jātijñānārthaṁ pṛcchati "kastvaṁ" iti। yadi tam eva na jānāti tarhi "viṣṇo" ity eva sambodhanā na syāt। "tvam akṣaram" ityādi ca॥31॥
He asks “Who are you?” only for the sake of knowing another aspect of the nature. Just as someone, even knowing a name or the like, may ask “Who are you?” to know the class or nature. If he did not know him at all, then the address “O Viṣṇu” would not apply. And likewise the statement “You are the imperishable” and so on.
Gīta Tātparya 11.31
The question is in regard to specific qualities and actions concerning Lord Viṣṇu.
viśeṣaguṇakarmaviṣaya eva praśnaḥ। "viṣṇo" iti sambodhanāt ॥31॥
The question concerns only specific qualities and actions, as inferred from the address "O Viṣṇu".
