It's in the episode The Wannabe in the Weeds. Brennan sings at the open mic night as Pam Nunan tries to shoot her, but shoots Booth instead.
The Wannabe in the Weeds is the fourteenth episode of the third season of Bones.
In this episode, Brennan and Booth investigate the killing of an aspiring singer, and Booth attracts a groupie.
For a guide listing the titles and air dates for episodes of the TV series Bones, go to EPGuides.com.
Watch the latest episodes of Bones on FOX.com.