What does it mean when scientists say that living organisms share a universal genetic code
All living organisms have a shared ancestor deep in the past, so all living organisms are related to some degree. We might share 99.8% DNA with chimps, but we also share maybe (just a guess, I don't remember the exact number) 24% DNA with lettuce. If all living organisms are related, than their genetic code is universal - one and the same for all organisms.