Already in Chapter 1 we see extraordinary bond between Emma and Mr. Knightley. Emma is girlishly playful with Mr. Knightley, and they are allies in trying to humor Mr. Woodhouse.

In Chapter 4 Emma reveals that she thinks Mr. Knightley is a picture of perfection, when she talks to Harriet about manners.

In Chapter 5 Mr. Knightley praises Emma in a conversation with Mrs. Weston, and his attitude is that of a protector, not of a lover.
In Chapter 8 they argue and I think there is no indication that they are anything else but friends.
In Chapter 12 they make up, Mr. Knightley says "my dear Emma", and they shake hands.
In Chapter 15 there is extraordinary show of intimacy, like a married couple, while the others were variously arguing and recommending, Mr. Knightley and Emma settled it in a few brief sentences: thus -- "Your father will not be easy; why do not you go?" "I am ready, if the others are." "Shall I ring the bell?" "Yes, do.".

But the first real signs of the attachment come in Chapter 26. Emma praises Mr. Knightley, and his reaction shows gratification :-) "Nonsensical girl!" was his reply, but not at all in anger. Then Mrs. Weston explains her theory about Mr. Knightley being in love with Jane Fairfax, Emma refuses any possibility of such an attachment, and she completely forgets Frank Churchill, with whom she is supposedly in love. LOL! With mixed feelings, she seated herself at a little distance from the numbers round the instrument, to listen. Frank Churchill sang again. They had sung together once or twice, it appeared, at Weymouth. But the sight of Mr. Knightley among the most attentive, soon drew away half Emma's mind; and she fell into a train of thinking on the subject of Mrs. Weston's suspicions, to which the sweet sounds of the united voices gave only momentary interruptions. Her objections to Mr. Knightley's marrying did not in the least subside. She could see nothing but evil in it. It would be a great disappointment to Mr. John Knightley; consequently to Isabella. A real injury to the children; a most mortifying change, and material loss to them all; a very great deduction from her father's daily comfort; and, as to herself, she could not at all endure the idea of Jane Fairfax at Donwell Abbey. A Mrs. Knightley for them all to give way to! No -- Mr. Knightley must never marry. So it is clear she cares more about Mr. Knightley than about Frank. Here is a part where Mr. Knightley reveals his feelings: she is looking at him, and he is immediatelly drawn to her. Presently Mr. Knightley looked back, and came and sat down by her.

Then in Chapter 28 Mr. Knightley changes his mind to come in after Miss Bates says that Frank is there as well as Emma. Mr. Knightley is jealous of Frank!

In Chapter 33 Mr. Knightley talks to Emma and Mrs. Weston, but he tellingly addresses Emma in the following exchange: ...Oh! no, upon my word I have not the smallest wish for your marrying Jane Fairfax or Jane any body. You would not come in and sit with us in this comfortable way, if you were married." Mr. Knightley was thoughtful again. The result of his reverie was, "No, Emma, I do not think the extent of my admiration for her will ever take me by surprize. I never had a thought of her in that way, I assure you." LOL! Did the extent of his admiration for Emma take him by surprise?
In Chapter 34 Mr. Knightley abuses Frank's handwriting. "I do not admire it," said Mr. Knightley. "It is too small -- wants strength. It is like a woman's writing." LOL again!

In Chapter 38 Mr. Knightley plainly shows his changed attitude toward Emma "Brother and sister! no, indeed."