I caught this dialogue on TV:
A: Who was that guy you spoke at the parking lot with?
B: How'd you known?
The second sentence, as I understand, is a contraction of "How had you known?" It seems to me that Present Perfect should be used here—"How have you known?" because the situation is unfolding now.
I can see using "How'd you known?" in a dialogue like this: "– I didn't support him, because I knew he was a betrayer. – How'd you known?" But I can't justify using it in this dialogue: "– Bad news, the game was postponed. – How have you known?"