There are a few big lessons in this video. Despite the snickers in the auditorium, and despite the bewilderment Sameer must have felt upon hearing what he probably thought was "numbnut," he stayed calm on the outside, and he stayed focused on trying to decipher the word. He didn't let the outside distractions take him away from his task. And when Sameer wasn't sure of the pronunciation, he pronounced what he had heard very clearly. Once he did this, it became obvious to Dr. Jacques Bailly, the pronouncer, that Sameer had misheard the word. A simple clear repronunciation of the word, and Sameer was good to go, much to his relief and much to the crowd's amusement and delight.
Let Sameer's example guide your demeanor while onstage. If you suddenly get a word you don't recognize, stay calm. An epiphany may be just a few questions away. Also, make sure to communicate with the pronouncer and especially the judges as clearly as possible. And if you don't know what you heard, communicate that fact clearly as well.
(By the way, "numbnut" is not a word found in Webster's Third New International Dictionary, the source of all words used in the National Spelling Bee. It is, however, informal slang, and not a terribly complimentary word!)