“瞧” means “看”, but "看" has more meanings other than "to see" "to watch". "看" also means "to judge" "to estimate" e.g. 看病 看风使舵 means “to visit" e.g. 看望 看朋友 means ”to think“ e.g. 看法

瞧 = glance 看 = look, watch. In other words, 瞧 has a shorter duration than 看

瞧，更加口语化。 看，相对来说更正式一些。

“瞧”较口语化，且都可以用“看”来代替，但“瞧”基本上不能和其他字组成词语或词组。 “看”的用法比“瞧”广泛得多得多，能和其他字组成非常多的词语和词组，不能用“瞧”来代替。如：看书、看电影、看报(纸）、看望、看法、看重、照看、看待、看中、偷看、好看等等。 学习中文的外国朋友们，如果你们分不清区别的话，那就都用“看”好了，绝不会出错。

At most time, they don't have any difference on the meaning. I think “瞧” is just like a dialect. The people live in Northern of China are prefer to use it...but if you mean you watch/look something for a long time (not just a glimpse), then you can't use 瞧 and can use 看 only. For example, you can say 我在看电视 （I'm watching TV）but you can say 我在瞧电视。