Specifically, discovers that Blue (Kwan) and Lucas Adams have written out the lyrics to the song on a piece of paper so they can sing along during a surgery. She mocks them for needing a "cheat sheet" for the lyrics.
If you are looking for the exact subtitle line or the context of the word "paper" in this episode, it is most likely referring to this specific interaction: : The interns are in the scrub room or the OR. Grey's Anatomy subtitles English S19E02
: Jules notices the paper and quips about them needing the lyrics written down to keep up with the surgery's "tradition." Specifically, discovers that Blue (Kwan) and Lucas Adams