***SPOILER ALERT***
During an interview following the Batwoman finale, the location was revealed (at least one of the locations- some more may be determined later):
During an interview with the International Business Times following Batwoman’s season finale (which featured a major DC reveal), showrunner Caroline Dries revealed the Superman/Batwoman crossover will take place in Smallville, which is where Superman & Lois will be set. “I have a little bit of research, but they don’t have any scripts out yet, like that’s been released, so nothing’s been shot,” Dries explained. “So obviously I know about ‘Superman & Lois’ and I know it will be taking place in Smallville and all the rest is to be determined, but it’s going to be a great challenge because those crossovers always end up so awesome.”
Source: ScreenRant