有兩樣木 Do You Know Two Woods
八戒道：「一發不曉得。」行者道：「你自幼在山中吃人，你曉得有兩樣木麼？」八戒道：「不知。是甚麼木？」八戒道：「一发不晓得。」行者道：「你自幼在山中吃人，你晓得有两样木么？」八戒道：「不知。是甚么木？」
逐句解 Line by line
Bajie said, "I do not understand a word of it."
He is not being difficult; he genuinely has not followed the classical tag. 一發 here means altogether or all the more, so the sense is that the last remark has left him further at sea than before.
Pilgrim said, "You spent your youth in the mountains eating people. Do you know that there are two kinds of wood?"
A magnificently rude opening to a teaching parable, and true — Bajie was a man-eating mountain fiend before Guanyin recruited him. Pilgrim is about to explain manners using timber, on the grounds that timber is the kind of thing a hill demon might have noticed.
Bajie said, "I do not know."
Three characters, and no defensiveness at all. Bajie's willingness to admit ignorance is one of his genuinely likeable qualities.
"What woods are they?"
And he takes the bait, which is what the parable needs. The question is split off into its own sentence to give the answer room to arrive.
Pilgrim switches teaching methods here, and the switch is the point. The classical quotation failed, so he reaches for a parable made of things Bajie has actually handled. Anyone who has had to explain an abstraction twice knows the move.
The setup also quietly reminds us who these pilgrims are. Bajie ate people. Pilgrim says so casually, as one might mention a previous job. The novel never lets its converted monsters forget what they were converted from, and it usually raises the subject for a laugh.