Tripitaka, seeing her, called out: "Eight Rules! Sha Monk! Wukong said just now that this wilderness held no one — but look, there's a person coming out over there!"

Here is the irony the whole chapter turns on, and it takes one sentence. Tripitaka quotes Wukong's own report — there is nobody out here — and treats it not as grounds for suspicion but as grounds for wonder. The fact that should have set off every alarm is the fact he finds charming. On the reading: this 那裡 points at something he can already see, so it is the pointing nà, "look, over there", not the questioning nǎ lǐ, "where", that has turned up several times already. The 了 in 見了 and 來了 marks the action done.

Said Eight Rules, "Master, you and Sha Monk sit tight — let old Hog go and take a look."

老豬 (lǎo zhū), "old Hog", is how Bajie refers to himself throughout the novel — mock-humble and quietly boastful at once, the way somebody says "leave it to your old dad". 坐著 keeps the other two sitting, 著 as zhe. And note who volunteers. He has not seen her face yet, and he is already on his feet.