Honorifics for Knighthood
[Sir] is the common male honorific for [knighthood]. But it is wise to know the [knight] in question's wishes. Many male knights Such as [Deigo] have chosen the traditional male Spanish honorific of [Don], while some knights use still other variations such as the modern [Syr] or [Ser].
Some female knights use it as well, as the alternative, [Dame] historically sometimes meant the wife of a knight, was a title by proxy, not directly upon the recipient.
At the end of the day it's all a matter of choice.