Yes AND no.
Yes because when Thorin, Bilbo and the others went into his lair, he deliberately laid on his stomach on his treasure. Why else; to defend this weak spot!
No because he forgot. Bilbo tricked Smaug twice into revealing it.
The first was during his conversation with Bilbo. Smaug was very polite with Bilbo listening to his riddles. Convinced that Bilbo did not mean him any harm, Smaug rolled over on his back. Bilbo saw the spot where the scale was missing somewhere on Smaug's chest.
The second time was when Smaug realised that Bilbo ran away with a golden two handled cup. This pushed Smaug's infuriation to its boiling point. He started destroying things and eating the dwarfs ponies and when he got to Long Lake, he was flying so high that the chink in Smaug's armor was visible. Bard the Bowman shot him in that very spot, Smaug didn't see it coming.
Smaug was a dragon.
esgaroth
Smaug only appeared in the Hobbit, where he was killed and he never appeared again (because he was dead). So smaug was not in the Lord of the Rings trilogy, but he was in the Hobbit.
Smaug is finally defeated when Bard the Bowman, a skilled archer from Lake-town, learns of the dragon's weak spot—a missing scale on his underbelly. Using this knowledge, Bard shoots a precise arrow that strikes Smaug in the vulnerable area, killing him. The death of the dragon leads to the release of his hoarded treasure, which becomes a pivotal point in the story and sets off a series of conflicts over the riches.
because he tells smaug he is Barrel-rider
The dragon Smaug stole it.
Who is Smaug
Smaug was a dragon.
Smaug takes a snooze. Z Z Z Z Z (Smaug)
Bard shoots Smaug with his black arrow.
Smaug the Golden (with some red I believe).
esgaroth
In "The Hobbit," Bard the Bowman knew where to aim the black arrow because he had learned about Smaug's weak spot from a thrush that overheard a conversation between Bilbo and the dragon. The thrush revealed to Bard that Smaug had a missing scale on his underbelly, which was his only vulnerable area. Armed with this knowledge, Bard skillfully targeted the weak spot, ultimately leading to Smaug's demise.
Smaug only appeared in the Hobbit, where he was killed and he never appeared again (because he was dead). So smaug was not in the Lord of the Rings trilogy, but he was in the Hobbit.
Smaug is finally defeated when Bard the Bowman, a skilled archer from Lake-town, learns of the dragon's weak spot—a missing scale on his underbelly. Using this knowledge, Bard shoots a precise arrow that strikes Smaug in the vulnerable area, killing him. The death of the dragon leads to the release of his hoarded treasure, which becomes a pivotal point in the story and sets off a series of conflicts over the riches.
because he tells smaug he is Barrel-rider
Smaug has never smelled anything like Bilbo and he cannot place it.