I just bought a 1999 jeep cherikee larado. it has a vacume line coming from top of trans. that is blocked off. I need to know where it goes

Noobie...... simmer down. Posting the same question over and over isn't going to help. That isn't a vacuum line. It's just the breather for the transfer case.

reckon why someone blocked it off with a bolt?

Because there are tons of stupid people who try to work on vehicles.........

Is it important to make sure its clear from blockage?

Yes. If not you can blow seals