Make thyself sick - “Feign thyself to be ill.” (Compare 2 Samuel 14:2.)
That I may see it - He was to feign that he could not fancy anything that came from the kitchen, but that if he saw it cooked he should be able to eat it.
Related Commentaries of 2 Samuel 13:5
2 Samuel 13:5
5 And Jonadab said unto him, Lay thee down on thy bed, and make thyself sick: and when thy father cometh to see thee, say unto him, I pray thee, let my sister Tamar come, and give me meat, and dress the meat in my sight, that I may see it, and eat it at her hand.