Yep Steve. "Sei lá" means "I don't know". It doesn't have a negative because it's like an Brazilian expression. It doesn't say exactly "I dont know", letter by letter it means "I know there". But the meaning is: I don't know and I don't care. E.g: -Onde está o Gabriel? (Where is Gabriel) -Sei lá. Tenho coisa mais importante para se preocupar.(I don't know. I have more important things to care about.

"Sei lá" is the same of "I don't know"! :)

Its means that you " Dont Know" , but its like a informal expression. You cant say this expression in a bussines meeting for example. But we use a lot in Brazil.

It's the equivalent of the English: 'Dunno'. Informal, colloquial, with the implication of 'Haven't a clue, and don't really care'.