John Gill Commentary 2 Samuel 13:5

"And Jonadab said unto him, Lay thee down on thy bed, and feign thyself sick: and when thy father cometh to see thee, say unto him, Let my sister Tamar come, I pray thee, and give me bread to eat, and dress the food in my sight, that I may see it, and eat it from her hand." — 2 Samuel 13:5 (ASV)

And Jonadab said unto him Being a subtle man, he presently formed a scheme to relieve him, and open a way for the enjoyment of what he desired:

lay yourself down on your bed, and make yourself sick ; feign yourself sick, pretend that you are so, by lying down on the bed, and making complaints of one kind or another:

and when your father comes to see you ; as he quickly would, after hearing of his illness, being very affectionate to his children:

say unto him, I pray you let, my sister Tamar come, and give me meat ; here he is directed to call her not Absalom's sister, but his own, the more to cover his ill design upon her:

and dress the meat in my sight, that I may see [it], and eat [it] at her hand ; pretending that his stomach was very weak and squeamish, that he could not eat anything which his servants dressed for him, and which he did not see done with his own eyes.