Hi,
if i have like 1000 Synx @Bittrex, do i get automaitcallt the Gravity one? Or do i need to have them in mt wallet?
In theory, you could still get your coins, but the ball would be in Bittrex's court. They control your private keys. If they choose to run off with your Gravity, they can do that.
It's why you should always be using a wallet where you control your keys! As in, the main Syndicate client. Same for any other coin, for that matter.