Which psalm begins and ends with "O LORD, our Lord, how majestic is Your name in all the earth!"?

Answer: Psalm 8

Psalm 8 opens (v. 1) and closes (v. 9) with this line (KJV: "how excellent is thy name"). In between it asks, "What is man?"

“For the choirmaster. According to Gittith. A Psalm of David. O LORD, our Lord, how majestic is Your name in all the earth! You have set Your glory above the heavens. O LORD, our Lord, how majestic is Your name in all the earth!”— Psalm 8:1, 8:9 (BSB)