I have a 5 weeks old kitten, he was raised by humans and hardly saw his mother cat. He doesn't seem to know how to groom and clean himself. Is there any way to teach him how to do it?
have you tried making his coat wet so that he possibly starts licking himself intuitively? this should wake up his natural instincts ^_^
Something that worked for me is this:

Take a napkin (not a paper napkin - but something made from cotton or another form of fabric), and a bowl with lukewarm water. (The best way to determine the temperature is to simply stick your tongue in it - if the temperature matches your tongues temperature, you've hit it spot on!)

Roll up the napkin on your finger, stick it in the water, and clean your cat (with the coat - never agaisnt it) with the napkin. This gives it the feeling of another cat grooming him. (an additional advice is to put your head as close as you can to your kitten while doing it.)

Best of luck to you. Emotion: smile