Can Scheme's call/cc implement all known control flow structures?
In this answer, I'll take "expressible" to mean "macro-expressible" in the sense of Felleisen 1991, On The Expressive Power of Programming Languages. (Intuitively, a language feature is macro-expressible if you can define it as a local source transformation, without using a whole-program transformation.)

With this definition, the answer is no: delimited control is not macro-expressible in the lambda-calculus + call/cc. To express delimited control operators using call/cc. In order to implement the control delimiters (the reset part of shift/reset), you need some state to simulate the continuation marks, essentially to encode a stack to simulate the dynamic lifetimes of the continuation marks. 

However, delimited control is a universal effect, in the following sense. In his PhD thesis, Andrzej Filinski showed that any expressible side effect is encodable using either delimited continuations, or call/cc and a single cell of state. Roughly, an "expressible side effect" is any effect whose monadic type can be defined in terms of the types of the programming language.

Surprisingly, this idea seems quite interesting in practice. Over the last decade, Gordon Plotkin and John Power have advocated the idea of taking an algebraic semantics of effects theories: the idea is that you specify the side-effecting operations you are interested in, and the equations you expect them to satisfy, and then you can generically get a semantics by taking the free monad over this theory. 

Matija Pretnar and Andrej Bauer took this mathematical approach, and then implemented it in their Eff language to invent a new language construct dubbed "effect handlers": you can write code that uses a set of imperative features, and then give the imperative features a semantics by writing a set of handlers which say how to implement each effectful operation.