會唱個喏兒 A Very Deep Bow Indeed
那兩個喜道：「這個和尚卻好，會唱個喏兒，又會稱道一聲兒。」問道：「長老，那裡來的？」八戒道：「那裡來的。」那两个喜道：「这个和尚却好，会唱个喏儿，又会称道一声儿。」问道：「长老，那里来的？」八戒道：「那里来的。」
逐句解 Line by line
The two of them were delighted. "What a fine monk this is. He knows how to make a proper salutation, and he knows the right word to call us by."
Their pleasure is the mirror image of their earlier rage, and for the same reason: both are about form, not fact. Once again 喏 is rě, the salutation, and the diminutive ending softens it to something like a nice little bow. 稱道 is to address somebody by a title. He has passed both tests, and neither of them is about who he actually is.
They asked, "Elder, where have you come from?"
Here 那 is nǎ, the questioning reading — which, is where — and not the nà that points at a thing already in view. The character is the same and only the context tells you which; this chapter carries seventy-seven of them and twenty are questions.
Bajie said, "Where have you come from."
And there it is. He has run out of script. He repeats the question back word for word as a statement, and 那 is nǎ here too because he is parroting the interrogative exactly as he heard it.
This is one of the best sustained gags in the novel and it is built out of nothing but punctuation. The fiends ask a question; Bajie returns the identical words with the question taken out. He has memorised the greeting and nothing beyond it.
The reason it works is that Pilgrim briefed him on the opening and not on the conversation. Bajie was told how to bow and what to call them. Nobody told him what to say once they replied, and he is not equipped to improvise.
It is also a nice demonstration of how much a Chinese sentence rests on its final particle and its context rather than its word order. The question and the answer are the same string of characters. Only the reading of one of them shifts, and even that is the audience's inference rather than anything written down.