what does uncle hammer do when he finds out that tj has temporarily given away his jacket?

Did you mean when Stacy gives the coat to TJ? Uncle Hammar is upset about Stacey's "gift" of his coat to TJ, unlike Jeremy's gift, is not unselfish but instead was given ignorantly, "You care what a lot of useless people say 'bout you you'll never get anywhere, 'cause there's a lotta folks don't want you to make it." Uncle Hammer's decision to let TJ keep the coat emphasizes the importance of deeply considering that which you give away, whether it be clothing or friendship, because gifts have long lasting consequences.