It can certainly be done with time to spare in 2 hours. As you exit into the arrivals hall, simply take the escalator or the elevator up to the departures level. CO normally has one of the closer gates.

It will probably take you less than 20 minutes from the gate to the check in counter. You will be back airside within the hour. Everything is signposted very clearly and you will have no trouble finding your way around. HKG is a very efficient airport.