kibitzer (n.)

• admonisher
• adviser
• beholder
• busybody
• buttinsky
• bystander
• confidant
• consultant
• counsel
• counselor
• expert
• eyewitness
• gazer
• guide
• instructor
• looker
• looker-on
• meddler
• mentor
• monitor
• nestor
• observer
• ogler
• onlooker
• perceiver
• percipient
• pragmatist
• pry
• quidnunc
• rubberneck
• seer
• snoop
• snooper
• spectator
• teacher
• viewer
• watcher
• witness
• yenta