In a small saucepan on the stove over low to medium heat, simmer and whisk together the eggnog, sugar, cinnamon and nutmeg for about 3 minutes. Whisk constantly so the mix doesn't burn. You will see that the mixture will begin to get a bit frothy.
In the mean time, make yourself a cup of hot coffee.
When the eggnog mixture has been heated thoroughly add it to the coffee.
To make it extra delicious add some whipped cream and a sprinkle of nutmeg.
Notes
Sugar can (or not be) added depending on how sweet you want your latte. Eggnog on its own is quite sweet, so you may not need the extra sugar.