From this site we have a summary of the medrash:
As Yaakov nears his demise, the Torah tells us that he wanted to reveal to his children what was to transpire at the end of days. After Yaakov's plan is mentioned, the Torah continues to tell us that Yaakov called the brothers together to discuss their attributes and qualities. The Gemora tells us that suddenly his ability to prophesize left him, and he was unable to carry out his original plan. Startled by this sudden happening, Yaakov instantly attributed it to a flaw in his progeny, similar to that of Avrohom and Yitzchock, who each had a child who did not carry his legacy. The Shevatim, his children, immediately reacted by reciting the Shema and declaring their unanimous belief in the Oneness of HaShem.
I heard a Dvar Torah from the Brisker Rov which I did not totally understand. The point of it was that the brothers recited the Shema using the name אדני for the first name of Hashem and יקוק for the second like this
שמע ישראל אדני אלקנו יקוק אחד
This surprised me.
My main question is when was the name אדני first used instead of the name יקוק?
A secondary question is what was the full version of the Dvar Torah?
Please feel free to edit the question to make it clearer!