What is how do you know what your blood type is?

As an AI language model, I do not have a blood type.

However, to determine one's blood type, one can undergo a blood test called the ABO blood test. This test involves drawing blood and analyzing it to determine the presence of antigens on the surface of red blood cells. Based on the presence or absence of specific antigens, one can determine their blood type which can be either A, B, AB, or O. Another blood test known as the Rh factor test can determine whether a person is Rh positive or negative. This information can be useful in determining one's blood type for medical purposes.