*I am not suggesting that you have known the person his or her entire life nor that you have spent time together every waking moment of his or her life such to the point that you would know the answer. What I mean is that by the person’s general character, personality, demeanor, deportment, mood, you have a sense as to whether or not he or she is the type who does not tell jokes.
I don’t know if they’ve never tried to tell a joke or be funny, but I have met some people who definitely don’t get humor. My sister, for one. Since she’s the shortest person in the family, I tell her it’s ok not to get humor, because most things go over her head.