I have flight with stop in HK at 14:30 for 3:30 hrs. Is it possible to get out airport and see something in HK?
No. There's not enough time, even to go to nearby Tung Chung. Especially in the afternoon. Just leaving the airport, passing through immigration, and coming back, passing through security checks and immigration, would take you and hour and a half. Plus, you don't have 3.5 hours, but 3 hours – remember you have to be at your gate 30 minutes before departure.
When I lived in Tung Chung, a few years ago, I had a couple of times two business trips back to back. I would go home, change bags, and go back to the airport, in less than an hour. But conditions were different. I don't need to pass through an Immigration counter (I use the eChannel), I know my way around the airport, and a blue taxi (for Lantau island) would take me home and back to the airport in 5 mn.
3.5 hours is hardly any time (you can get somewhere but you still have to get back, go through outgoing immigration and security with enough time to be comfortable), but you could see if there is anything interesting (to you) going on at Asiaworld Expo Centre- there is often a trade show going on and if you happen to be deep in the fresh fruit, eyeglass frame or lingerie business it might even be exciting. It's one stop on the Airport Express .. I think about HKD5.. cheap anyway. Usually trade only admission.
Otherwise, it's easy to spend a few hours at the airport. If you go to arrivals you may find less expensive food etc. than with the trapped folks in departures.