1. Is there any way to generate bitcoin address offline without the help of the internet ?
Yes, I've read about this some time in the past, though I didn't really pay attention to understand most parts of the article, but I know that some service have made it possible to even send and receive bitcoin without internet connectivity.
You can google this to find out how.
2. Since Bitcoin launched is there any wallet that supports auto editing the gas fee of Bitcoin straight from your android or IOS machine?
Yes, you download and try Mycelium wallet, the app is available both on Android and iOS devices, the wallet offers the ability to adjust the amount of bitcoin you want to spend as a gas fee to have your transaction confirmed on the blockchain, but remember that the lower the fee you choose to pay, the longer your transactions stays without confirmation, and in some cases, you might end up not getting your transaction confirmed if the fee set is extremely low.
3. Does high gas fee means faster-sending speed on bitcoin wallet?
Yes, the higher the bitcoins you choose to spend as a gas fee for your transaction, the faster the transaction will get confirmed on the blockchain.