I enjoyed reading the linking of the three chapters.

There's another line that might add something;

There is an anxiety, a curiosity in what one feels for Emma.

Perhaps he's been struggling to analyse his feelings for Emma.

Mrs Weston's "So do I." is in response to Mr Knightley's " I wonder what will become of her."
So I think It's Mr Knightley only wondering about what he feels for her.
He's curious about it means he hasn't settled to the quality yet.