וַיָּבֹ֥א אֶל־אָבִ֖יו וַיֹּ֣אמֶר אָבִ֑י וַיֹּ֣אמֶר הִנֶּ֔נִּי מִ֥י אַתָּ֖ה בְּנִֽי׃
И он пришел к отцу своему и сказал: 'Мой отец'; и сказал он:'Вот я; кто ты, сын мой?'
Radak
ויבא אל אביו, into the room where he was lying down. He called to him: אבי, seeing he (Yitzchok) could not see him.
Radak
?מי אתה, seeing that he had addressed him simply with the word אבי, he had doubts about whose voice he had heard he had to ask: “who are you?”