Translation:I do not know anything about his past.
I'm not a native, but my German teacher said "wissen" is used when you know something as a fact, and "kennen" is when you know of something or someone.
You could translate "wissen" as "to know," while "kennen" could be "to be acquainted with."
"Ich kenne die Antwort" = "I know the answer." "Ich weiß, dass die Antwort nein wird" = "I know that the answer will be no."
It takes some practice to get a feel for it, but I hope this helps ^-^