This link might be very useful to you:
Letters to and From the Watchtower Society Concerning Noah's Flood
They show how a (now former) JW outlines the scientific issues about the flood and shows the WT responses.
Also this link: The Vapor Canopy Hypothesis Holds No Water might be useful.
Classic questions to ask:
- How did animals that only live in one part of the earth, like kangaroos, get to Turkey? Even more importantly, given the 'new' oceans the flood created, how did they get back to Australia?
- If the ark was above the tops of mountains then they were above Everest. And you'd need warm clothes as it is so cold and an air tank to breathe. How did Noah, likely dressed for a middle eastern climate and his family and the animals survive in those conditions? How come their water didn't freeze?
- If there was a water canopy then the temperature around the earth would have been warmer. How could you have the polar regions in that warmer environment? Ice core samples go back long before 2,370 BC (when the WT claims the flood happened).
And so on and so on.
I think the WT are pretty much the last large group to believe in the water canopy idea.