There are 33.814022 ounces in a liter. You would not need to necessarily memorize this conversion as you may not need to use it very often. If you do a lot of science work or are interested in a field like that, or perhaps if you bake a lot then this would be good to know off hand.
In order to find out the amount of ounces in any number of liters, you just multiply the number of liters by 33.814022 (though you could shorten it to 333.8 most of the time) and you will know how many ounces are in the amount of liters. So if you have 2 liters, you multiply 2 by 33.814022 and you get 67.628044. That is how many ounces are in 2 liters!