1)
What is knowing that "Atah Shimcha Hashem"?
1.
Radak: You and Your name are alone; there is no one other than You - "ba'Yom ha'Hu Yihyeh Hashem Echad u'Shemo Echad" (Zecharyah 14:9). They will know in their hearts that there is no god other than You; only You are Kel. Also, they will mention only Your name, and not that of other gods.
2)
Why does it say "Elyon Al Kol ha'Aretz"?
1.
Radak: Everything is under His hand and in His jurisdiction.
2.
Malbim: Elyon is relative to something underneath. Something can be Elyon to what is below it, but something else is Elyon over it. They will know that nothing is Elyon over You, for You are the Head of all causes and results.
