what chapter does George ask Lennie if he remembers the hiding spot if anything bad happened at the new job?

To answer this question, take a look at chapter 2. In this chapter, George and Lennie meet Curley for the first time. Curley takes an instant dislike to Lennie, acting very aggressively and hostile towards him. Although Lennie is large and strong, he has no desire to make an enemy of Curley and certainly does not want to fight him.
In response, George gets very worried and asks Lennie about the hiding place that he highlighted to him in chapter 1. Specifically, he asks Lennie if he can remember the place:

You remember where we slep' last night? Down by the river?

George then tells Lennie that if anything bad happens, he must go there and wait.
This is significant because it demonstrates George's sense of care and compassion towards Lennie while also foreshadowing the accidental death of Curley's wife later in the novel.