The word “kennen” is used primarily for people, things and places. This word expresses familiarity with something that’s been experienced or that the speaker has had contact with. (For grammar nerds: “kennen” is always followed by an accusative object).
Examples
Ich kenne ihn. I know him.
Ich kenne Paris. I know/am familiar with Paris.
Ich kenne den Plan. I know/am familiar with the plan.
Ich kenne Photoshop nicht so gut. I don’t know Photoshop so well.
Wissen
The word “wissen” is used for abstract information or factual knowledge (and is usually followed by a longer phrase).
Hey. My name's Stephan. I wrote this blog post. What I also did: I filmed myself teaching German to some absolute beginners! See how that went...
Examples
Ich weiß wie es funktioniert. I know how it works.
Du weißt nicht was die Hauptstadt von Australian ist. You don’t know what the capital of Australia is.
Wir wissen es nicht. We don’t know.
In sum: Ich weiß dass du ihn kennst. I know that you know him.