Bitfinex, binance, yobit, hitbtc - BTC holders in these exchanges received BTG after the fork was initiated and the trading started in respective exchanges right? Wallets not active for deposit / withdraw.
The holders who had BTC in private wallets will transfer BTG to these exchanges once the wallets are active for trading.
or are these speculative tradings?
Please comment....
Yes. Yobit and HitBTC already giving out BTG to users and trading has started a few hours ago. These markets are not real BTG, instead these are futures trading (speculative, as you say). I've dumped my BTG on HitBTC as soon as I received it

Exactly, people who hold BTC in their own wallet cannot send/receive BTG yet because the network is not launched yet. Expect some movement in BTG prices (most likely go down though) when people actually be able to make transactions on BTG chain.