Jonas engages in typical playful activities with his peers during his childhood and enjoys playing catch, riding his bike along the river, and participating in harmless simulated war activities like good guys vs. bad guys. Some of the playtime activities are required for certain children like Asher, who is required to play catch to improve his coordination. Before Jonas is selected to be the community's next Receiver of Memory during the Ceremony of Twelve, he enjoys engaging in playful activities with his friends and lives a relatively carefree lifestyle. In addition to participating in typical play activities with his peers, Jonas also volunteers at various occupations throughout his community to have an idea of his future career interests. In Jonas's highly-structured community, which is founded on the concepts of Sameness, there is very little downtime and the children do not have the opportunity to express their individual interests or differences by engaging in specific hobbies. Therefore, Jonas does not have one specific hobby that he enjoys more than the rest and takes pleasure in typical childhood activities like riding his bike, playing make-believe games with his friends, and playing catch with Asher.

Jonas enjoys spending time with his friends playing games like the war game or tossing a ball around. However, Jonas doesn't have specific hobbies that he'd rather do more than anything else, and this is one of the reasons why he can't begin to guess where his placement will be at the Ceremony of Twelves. Some kids his age have a penchant for certain activities, like a talent for caring for people or fixing things. However, Jonas is pretty well rounded, very emotionally stable, and enjoys spending time with his friends. He also begins to develop a connection with the newchild Gabe, and it becomes apparent that Jonas is nurturing. However he has no special drive to be a nurturer or to care for the old. He is also very thoughtful and introspective, but he does not seem to have any driving interest in a particular subject or hobby that might lead him to a placement.

Jonas lives in a tightly controlled society.  Unlike most kids his age, he is not focused on one hobby.  He does a little bit of everything.

Hobbies as we know them don't exist in Jonas's world, but they do have volunteer hours.

As part of Jonas’s training, he has to volunteer in several different professions.  Jonas does not choose one.  Instead, he seems to enjoy spreading his volunteer hours around, doing a little of this and a little of that.

The freedom to choose where to spend those hours had always seemed a wonderful luxury to Jonas; other hours of the day were so carefully regulated. (p. 26)

Like most kids, Jonas plays ball and rides his bike.  These are not hobbies though.  He plays catch with his friend Asher because it is required exercise to help his hand-eye coordination. 

Jonas was glad that he had, over the years, chosen to do his hours in a variety of places so that he could experience the differences. (p. 29)

If Jonas has any actual hobby, it would probably be hanging out with Gabe.  He consoles Gabe and takes care of him, and even gives him memories—even though it’s forbidden.

Lowry, Lois (1993-04-26). The Giver (Newbery Medal Book) (p. 26/29). Houghton Mifflin Harcourt. Kindle Edition.