Is 看一看 equal to 瞧一瞧 in meaning?
Are they interchangeable?
In Northern China, 瞧 is the colloquial form of 看 and they are always interchangeable. I can't speak for Southern China though.
E.g.
I'm from Southern China, never say 瞧一瞧, people may understand you when you say that but definitely it sounds a little bit weird, at least to me.
I think 看一看 will be good everywhere in China
When I chat the informal way to say 看一看 is 瞄一眼(glance)
In a casual situation, 看一看 and 瞧一瞧 are quite the same and totally interchangeable. They are both acceptable in Mandarin, and Mandarin is valid for any Mandarin speaker, so we don't have to be too sensitive about the regional difference.
However, there exist situations where 看 and 瞧 have different meanings.
看一看电视
Watch the television.
[It can mean, "Have a look at what's playing", "Watch it just to relax", etc.]
瞧一瞧电视
Have a check on the television.
[This can hardly mean to watch what's playing, it can mean "check its function, quality (for repairing or purchase)", or "check the body of the television (if you want something)"]
So in this case, 看一看 means to watch (the play), while 瞧一瞧 means to check (the body).
The same goes for other "readable things" like the phone, the newspaper, the book, etc.
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If you want to know the deeper difference in Chinese literature, then I would say 看 means more vaguely than 瞧. Most of the time 瞧 can be replaced by 看. Sometimes 瞧 implies some emotion (the kind of emotion depends on the situation), while 看 implies less emotion but more emphasis on the action itself. Specific examples:
E.g.
我看见他了。
I saw him.
[The implication totally depends on other things like the dialogue, the environment and the tone. It can mean "I found him", "I met him", or "I saw what he did".]
我瞧见他了。
I saw him (and somehow my feeling was affected).
[Maybe it's scared, happy, shy, etc.]
你看一看。
See it.
[Same as above. It can mean "Have a look", "Check it", etc.]
你瞧一瞧。 Please see it (and I expect your reaction).
Again, 看 might able to mean the same, but it cannot imply more as 瞧 does by simply one sentence.