게 있는데

there's something...

→ 것+이
phrase Uncommon #11,478
there's something... 게 is a shortened form of 것이, meaning “thing.” This phrase often introduces something the speaker wants to mention or ask about.
KO: 물어볼 게 있는데요.
EN: There's something I want to ask you.

보내야 할 게 있는데

I have something I need to send.

— 순응자 (1971)

들어 봐, 잊은 게 있는데 그는 혼자가 아냐, 다섯이나 있어

Listen, there's something you forgot: he's not alone—there are five of them.

— 석양의 무법자 (1966)

얘기해 드릴 게 있는데 난 이미 모든 걸 다 알지

There’s something I want to tell you, but I already know everything.

— 안드레이 루블료프 (1966)

거기 무슨 재밌는 게 있는데?

What's so interesting there?

— 400번의 구타 (1959)

보여 줄 게 있는데

I have something to show you.

— Tune in for Love (2019)