Which episode features Penny giving Sheldon Leonard Nimoy's signed napkin?

The episode featuring Penny giving Sheldon Leonard Nimoy's signed napkin is “The Bath Item Gift Hypothesis.”

It is the eleventh episode of season 2 and the 28th episode overall, first broadcast on December 15, 2008. The story centers on Sheldon’s anxiety about exchanging Christmas gifts with Penny and his attempt to find a present of equal value.

Penny gives Sheldon a napkin autographed and previously used by Leonard Nimoy, the actor famous for playing Spock in Star Trek. Sheldon is thrilled because he believes the napkin contains Nimoy’s DNA. Overwhelmed by the gift, he gives Penny every bath-product basket he bought and hugs her—an unusually emotional moment for him.

A common mix-up is confusing the episode with another early-season title involving gifts or holiday events. The key identifying detail is not simply Christmas, but Sheldon’s reaction to the Nimoy napkin and his rare hug for Penny.