They are the same meaning though usually I hear the second one more.

They are similar. "Was it not obvious?" is unusual because it doesn't use the usual contracted form. The pronunciation is "Was it (pause) NOT (pause) OBVIOUS?" and shows extreme annoyance (..."you are SO STUPID ... was it NOT OBVIOUS? ..." "Wasn't it obvious?" is usual. The pronunciation is "Wasn't it OBVIOUS?"and shows moderate annoyance (...PAY ATTENTION ... wasn't it OBVIOUS? ...)

Tom is right. Often you will hear the sentence stress placed on "not". "wasn't it obvious" is the common use. "was it not obvious" is for when you're making your point stronger. Thanks, Stephen

Same, the first maybe is a bit more emphatic.

thanks a lot everyone