how much alcohol is cooked away in preparing agar agar?
There is a misconception that alcohol will easily burn off when used in cooking, and since pure alcohol has a lower boiling point than water, if you mix them, it is thought, the alcohol will burn off first. 

The reality is that when mixed together the situation gets more complicated and the new boiling point of this solution is neither that of pure alcohol (173°F/78°C) nor water (212°F/100°C) and will fall between depending on the ratio of the mixture (keeping in mind that you started with water in your alcohol). 

So if you want to cook with alcohol and burn more of it off it's best to do so before adding water. In your case you may want to cook down the liqueur first to remove more of the alcohol. If you combine them as you have been, you can assume that you'll burn off a similar ratio of water and alcohol from the solution.