This is one thing I need to do more often. I came from a school and industry segment (.Net) that very highly discourages reading other people's code, and even years later I feel guilty trying to read jQuery's source when I run into a weird edge case.
Is there projects out there that are easy for beginner code readers to grok? I've tried reading libraries you've all heard of, but even after an hour of jumping between files I still have trouble getting a view-from-10000-feet picture of how the project works.
That said, here are a couple suggestions. I'm not sure what you use other than C# (and Javascript?) so I'm just gonna link things from several languages.
redis-rb [1] is the 'official' Ruby client for redis. (For that matter, I've always heard that redis itself [2] is a good example of C code.) React's source [3] is rather difficult to figure out, but the team recently released a codebase overview [4] which might help. Alternatively, preact [5] is relatively straightforward, and IMO is a good example of structuring an ES6 codebase.
Rails [6] is ridiculously huge, and has established a bunch of its own conventions for file loading, but on the flip-side it is extremely well documented. To take a single bite of the elephant, take a look at its ActiveJob [7] sub-framework.
1: https://github.com/redis/redis-rb
2: https://github.com/antirez/redis
3: https://github.com/facebook/react
4: https://facebook.github.io/react/contributing/codebase-overv...
5: https://github.com/developit/preact