BERLIN—Volkswagen should have gone public in 2008 with the engine plan that sparked its diesel emissions scandal, a German court said on Thursday, as it set out its views on a test case brought by investors against the automaker. Volkswagen, which admitted in 2015 to cheating U.S. diesel engine tests, said it had fulfilled all its disclosure obligations and any compensation claims were unfounded. The 2015 admission sparked the biggest crisis in Volkswagen’s history and has cost the German company more than 32 billion euros ($38 billion) in vehicle refits, fines, and legal costs so far. The scandal has been traced back to 2008, approximately when Volkswagen started using software to control diesel engine emissions that was later ruled illegal when discovered by U.S. regulators. Whether investors can claim compensation for the plunge in Volkswagen’s share price after the scandal was exposed depends on whether it can be proven that …