Knowledge on both ends naturally. It's not like you can create a database, or a game, just because you know 3-4 programming languages no? Programming languages is basically just a medium to achieve the ending you'd really want, so it's naturally a requirement to learn on both ends. As for what programming language you'd need to learn, I doubt there's much difference between any major languages like Java, C++, Python, but if you want a list, just look up in google or you can check what I found.
Although our software knowledge is high, when we do not think about the sucture of Bitcoin, can our software knowledge pave the way for these thoughts, is it enough to just work on software? To be able to create something.
No, it may be a vague thing, but the will to work and improve on the structure you'd want to make is the foundation of making something, otherwise, you'd really just basically be copying and pasting other's foundation of blockchain into yours.