I dispute the scientific basis of your link.
All of the gold in a one-litre bottle of Goldschlager weighed a total of 12.9 mg...As there was a small amount of silver detected, this indicates that the gold isn't pure and therefore would be worth slightly less.
It's probably 23 carat gold leaf. 23 carat leaf is 95.8% gold. 12.9mg x .958 = 12.3582mg of pure gold.
There are 31,103.5 mg per Troy ounce. That means there are .000032151 troy ounces per mg. Gold is currently $12.26 per Troy ounce, so a single milligram of gold is worth 0.03942 cents. The amount of gold in Goldschlager, therefore, is worth $0.49 per bottle (48.712 cents as of 3:30 pm PST Oct 20 2018).