It's an impossible question to answer. It depends on which country one is native to, and still there is no agreement on what constitutes 'neutral.' In the US, broadcasters are all taught a certain style ( the style of which I find extremely annoying, but that's another topic ) which is considered neutral.

In my opinion, the word "neutral" with regard to accents is impressionistic, conventional, and subjective. Where I live, in Birmingham (England), some local people might say that a neutral accent was a standard southern England accent or perhaps the accent of a well-educated local who did not use too much street talk. Or they might describe such speakers as having "no" accent, which is a more common description, in my experience.

Nobody knows. There is something called "General American English" but I've seen arguments about whether it really exists. An interesting question is this: do I ever hear someone speaking and say "they really speak in a different way from me, and it's because I have an accent and they don't?" Nope. How often do I hear someone speaking and say "they speak in a different way from me, and neither of us has an accent?" Maybe sometimes.

BBC Radio 4 newsreaders are the most neutral to my ear. They bend their accent to an expected norm. They Might keep a bit of their original style but they will work towards "Received Pronunciation" or RP. Technically it is still an accent, that of the upper classes of south east England. It used to be regarded as the "correct" way to speak but now regional accents are regarded as equally "correct." National and indeed international broadcasts have to be widely understood and RP has the fewest deviations from the correct way to pronounce English. Of course, if you were upper class English, you might have had a lot of say in what that is.

hello, I am vietnamese student, i want to study english very much, can you help me ?