Currently nearly all of the documentation for Swift language and its key protocols and components, Foundation framework components is hosted on Apple Developer website. But I didn't find the place to post improvement suggestions when the documentation is incomplete or misleading, or needs clarification.
And it would be nice to clarify the status of this documentation, who is its owner and by whom it is maintained.
For things hosted on Apple's domain, suggestions should be filed at http://feedbackassistant.apple.com.
And as for TSPL specifically, it’s open source so you can submit issues or even PRs at GitHub - swiftlang/swift-book: The Swift Programming Language book.
Right, TSPL has been hosted on swift.org for long time though, I'd assume the OP is referring to developer.apple.com subdomain.
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For the Swift standard library and other projects under the Swift project umbrella, parts of the documentation are derived from the doc comments written in source.
You can head over to the relevant repositories and file issues and/or PRs to suggest clarifications--small pulls that make such corrections are absolutely accepted.
(Anything hosted at developer.apple.com, of course, can be edited/altered by Apple's documentation team per their internal processes and for any issues related to that you'd file feedback as @Max_Desiatov has said.)