The Jonas Brothers, Kim Clijsters, Rafael Nadal, Demi Lovato and others hold court tomorrow at the Billie Jean King National Tennis Center in Flushing. No, the JoBros aren’t playing tennis, just music. It’s part of the 15th annual Arthur Ashe Kids’ Day, which remembers the tennis great Ashe and his mission to help kids through the sport and education. “We love the fact that Ashe [got] kids involved with tennis and sports overall. He’s a great role model and a real icon both on and off the court,” Kevin Jonas tells The Post. “We’re really honored to be associated with an event that bears the name and legacy of Arthur Ashe.” In addition to the musical performances, top tennis stars will offer exhibitions and clinics — and kids can even find out how fast their serve is. It all happens from 9:30 a.m. to 4 p.m. (the big acts play in the afternoon; tickets, $10 to $20). For details, go to usta.usopen.org/ArthurAsheKidsDay. As for their tennis skills, Jonas admits, “We may not be the best players in the world, but we love the sport.” — Don Kaplan