Superstar duet! Demi Lovato and Alanis Morissette sing 'You Outta Know' This image appears in the gallery:American Music Awards 2015: 39 MUST-SEE Highlights From This Year's Show 38. Superstar duet! Demi Lovato and Alanis Morissette sing 'You Outta Know' Picture: Getty 39 images See the full gallery: American Music Awards 2015: 39 MUST-SEE Highlights From This Year's Show