There will never be a perfect balance between these competing needs, and the line will be pushed back and forth as long as there are humans to debate the issue.
Is there a "right to knowledge"?
I'm aware of rights to speech, thought, movement, conscious, religion, expression, assembly, association, etc. But I've never heard anyone claim, or read any charter/constitution/etc. that has a "right to knowledge" clause.
Is there a country which has enshrined a "right to knowledge"? Does it have any limits (alluding to what you mentioned, how does the right to knowledge interact with other rights)?
It's so fundamental a right that most places only enshrine more complicated versions of it as law. Most societies now even extend that right to offer control over the knowledge you store electronically or write down and the way other people get to use "your" knowledge.
When we seek to impose privacy limitations on the data that others can gather we're curtailing those rights to some extent. We're telling them there are specific things they can't know and that does limit their freedom in a very fundamental way.
it's the right to observe somebody else without their consent: it's quiet scientific observation that tries not to disturb the observed which is impossible in the quantum level but very realistic in the day to day classic (non-quantum) level
tl;dr: the right to create knowledge i.e. do science
The point, restated, is this: When we pass laws that say "There are factually true things that you are not allowed to know under penalty of law" we had better be damn sure the tradeoff is worth it. Sometimes it will be, sometimes it won't. The exact line will always be ill-defined.
It can in several variants. Freedom of expression probably can't without private speech.
The United States, for example, wouldn't exist if Thomas Payne hadn't been able to publish his pamphlets anonymously.
Yes. Freedom of speech doesn't require privacy in most constructions as it typically concerns, first and foremost, publicly-made political speech. This finds its way into U.S. law through the expansion of the First Amendment's protections by its press and religion clauses [1].
[1] https://law.justia.com/constitution/us/amendment-01/06-diffe...
Suppose you're Thomas Paine and you want to advocate for the independence of America from Britain, and that Britain doesn't allow the government to punish anyone for what they say, but does prohibit anyone from publishing their writings anonymously.
Then everyone knows exactly who Thomas Paine is, and even if there is no law against writing those things, there is now a constable poking into his business looking for some other pretext to arrest him, several legislators drafting bills that would negatively impact his livelihood and which will quietly be withdrawn if he would simply stop publishing such things, and a variety of private enterprises who now refuse to have anything to do with him in any capacity because they have business before the crown and fear any public association with their critic.
How is it free speech if you're still getting punished for it?
From my perspective, you simply can't speak freely if the government (or your neighbors) might murder you for saying things they disagree with.