In the Name of God, the Compassionate, the Merciful.
Hi!
A: Oh, you knew it was a joke, didn’t you?
B: Yes, I knew it was a joke. It was your first real joke.
A: Hooh, a good one. ← Original text
B: Well done, Chips, that’s marvelous.
I don’t hear any subject/verb there. Of course, he’s just referring back to his joke.
The first “word” is just a sound. It’s not clear, but “Oh” makes the most sense. I’ve never seen “Hooh”.
And, congratulations to CHIPS on making a joke. That is a rather sophisticated mental process.