Once I read that the sentence ending particle "ね" is not only used when we are asking for an agreement or expressing our agreement, but it is also used when we are talking about our experience, our thoughts even if the listener doesn't know anything about it. Can someone make it clear? I don't understand how to use ね with that meaning.
This is basically the same post as https://japanese.stackexchange.com/a/27583
I'm going to explain about sentence ender ね (not interjectional ね).
It has several usages and some of them can be interpreted like English tag question. But the function that's shared by all those usages is to indicate that information accompanied with な or ね is your impression or conclusion through observation (including recollection or imagination of your own) in the moment.
(Difference between な and ね is that the former is cut out for monologue while the latter is aimed at other people. If you use な in speaking to other people, it sounds rough.)
For example, when you are talking to your friend on the phone, you can say 声きれいだね (which can be translated to "you have nice voice, right? / indeed / after all") . However, if you say 髪きれいだね ("you have pretty hair…"), s/he will be surprised and respond as "Are you watching me!?".
That's to say, you can't use it like tag question unless you share the context with the listener. (To say another example, In order to be able to say おいしいね as a tag question, the listener has to be actually eating it, not only present there.)
On the other hand, 髪きれいだよね works well even in that scene because よね can refer to what is not present in the context.
In the situation where you can say 声きれいだね, if you nevertheless use よね and say 声きれいだよね, it feels a little uncertain compared with one without よ.