I've never heard "sah" used for "I don't know". Sah is similar to "you know" as in valley girl speak.

Hey, yesterday you know, I want to the mall you know, and there was this sale, you know, it was totally cheap, you know, so I bought 3 pairs of shoes, you know, aren't they great!?

In Japanese you can replace every "you know" with "sah".

You can put "sah" at the end of sentence when you don't know something or are contemplating but I wouldn't translate it in that case as "I don't know". Rather more like "Hmmmm...." as in "I wonder" like the feeling this emoji is trying to express https://www.google.com/search?q=hmmm+emoji