I plan to fly via ICN from YYZ to BKK. Can I take a bottle of alcohol that I buy from the Duty Free in YYZ to BKK via ICN? Would the security at ICN allow me to carry it?

The rules for carrying duty free liquids through security at Inchon are the same as in the US (Bringing Carry On Duty-Free Liquids with Connecting Flights).

From the Inchon International Airport website:And the Korean Air Incheon International Airport information:

assuming the actual product or the quantity is not prohibited to bring into ICN then you should have no problem.

I believe most countries have consistent security procedures that will allow liquids bought at a duty-free shop to pass through security screening checkpoints as carry-on IF it is sealed in a tamper-evident bag AND it is in original retail packaging AND it is unopened.

In some countries there is no longer actual "international transit" which means you must clear immigration and customs and then go through security screening again to make the connecting flight and therefore you might be required to put the bottle in checked baggage because the connection airport has limitations on liquid container sizes allowed through the screening checkpoint.

If you can put it in checked baggage you should have an even greater chance at success.

Your airline should be able to verify what rules apply for your particular situation.

Thank you TWA and Section. I am flying AC to ICN and then transit to Asiana to BKK. I do not enter Korea. I am actually hoping that I make my flight to BKK because AC keeps changing their flight times.

Just finished some very long trips flying with Delta from STL to INC (via SLC), and onward (with KE) to CNX, and return 3 weeks later from CNX via INC, DTW, back to STL,
I found the Korean transient security personnel at Inchon's Terminal 2 to be highly unfriendly, uncooperative, and frankly very rude. My wife and I are both in our eighties (definitely considered elderly), and are not accustomed to be told in a very loud voice to remove our hats,belts, shoes, jackets, and "everything which can be removed", in an airport TSA environment (especially since we came out of a known secure area and going back to a secure area) !!!
I personally was chastised loudly by two Korean TSA agents (one male; one female), across the security table, because I had overlooked a cloth hanky and two wrapped wooden toothpicks in my shirt pocket. Also, there was no attempt made to help us obtaining any of the inspection trays, which had to be picked up from the bottom of a table, and then placed in separate transport trays/bins. In my case three trays, and for my wife four. This was very surprising since Asian cultures normally treat elderly people more respectfully, and usually offer any assistance and courtesies if someone appears to require help.
Finally, there was a lot of walking required from the incoming Delta gate area, to transient security, and then onward two our Korean Airline connecting flight onward to Thailand. Should we be privileged to live much longer, and consider perhaps another trip to Asia, we will definitely avoid transiting the airport at Inchon Korea. We are very disappointed to having had such a negative experience, but wanted others to know what elderly travelers may encounter, if transiting through the very large international airport at Inchon Korea.