There's no answer to this question; it's like asking how many dollars are in 32 degrees Fahrenheit. A liter is a unit of volume. An ounce is a unit of weight. A similar question would be how many fluid ounces equals 3 liters. There are approximately 101.422 fluid ounces in 3 liters.
By US measurement, 16 ounces to a pint, 1 liter = 2.113377 pints, and 3 liters = 3 x 2.113377 pints = 6.034 pints By imperial (British, Canadian, etc.) measurement, 20 ounces to a pint, 1 liter = 1.759754 pints, and 3 liters = 3 x 1.759754 pints = 5.28 pints 3 litres = 6.34012926 US pints