The episode you are looking for is Season 2, Episode 13, titled " Mr. Monk and the Missing Granny " . Episode Synopsis

In this episode, an elderly woman named Mrs. Parlo is kidnapped from her home by masked intruders who leave behind a spray-painted lightning bolt. Her granddaughter, law student Julie Parlo (played by Rachel Dratch), hires Adrian Monk to find her. In exchange for his help, Julie promises to use a clever legal loophole to help Monk get reinstated to the police force. The case takes several bizarre turns:

The chair was personally handcrafted by Thomas Jefferson in 1774 and is worth over two million dollars. Where to Watch