When George finds Lennie, what does Lennie expect him to do? How does George respond?

I assume that you are talking about the part right at the end of the book.  This is where Lennie has gone back to that place by the river after he has killed Curley's wife.

Lennie expects that George will give him hell.  He asks George if George is not going to do it.

George says that he will not, but Lennie really wants him to.  So George goes with his usual spiel about how much better his life would be without Lennie around, but his heart isn't in it because he knows he has to kill Lennie.