Extremely Loud & Incredibly Close (2011)

A young boy, Oskar, is trying to cope with the loss of his father. His father was a jeweler working on the 105th floor of the World Trade Center in New York city. He is at work on the tragic day of September 11, 2001 when the twin towers collapse. Oskar hears his father's final answer machine messages, left on that fateful day, which he conceals from his mother. A year later, he discovers a key in his father's belongings and, as he used to do with his father, embarks on a scavenger hunt to find the matching lock. He meets lots of people along the way and documents his journey in a scrapbook.

IMDB

Storyline
A nine-year-old amateur inventor, Francophile, and pacifist searches New York City for the lock that matches a mysterious key left behind by his father, who died in the World Trade Center on September 11, 2001.