I would reckon that he probably has a fair bit of knowledge about Kryptonian science by way of the Fortress, but that doesn't necessarily translate to knowledge of Terran science/technology. He can build/repair the robots in the Fortress, but that doesn't mean he knows how to change a hard drive. Stone knives and bear skins, as it were.
My preferred understanding of Superman's intelligence is that he probably has a very strong ability for raw data processing and memory and things like that, along with an understanding of super-high technology, but he lacks the brilliance of someone like Lex or Bruce that would let him draw creative conclusions or invent things. But Superman is a character that's been around for nearly a century by now, with dozens of different writers and various Elseverses and so on. There are a lot of different takes on him.