9 week old Kitten doesn't clean his bum/hair after peeing. How do i train him to clean himself prope

He leaves wet marks everywhere after peeing. 

got him from a shelter. he was abandoned by his mother. 

I would use a wet paper towel to pat him off.  The wetness might encourage him to groom himself.  

What kind of litter do you use? I know some cats have issues with soiling themselves but it's usually fecal matter and not urine. I wonder why he would get in touch with the urine while using the box?

Here's an article about cleaning kitty bums which could help with your issue as well - 

 [article="32464"]Be Kind To Your Cats Behinds Dirty Cat Butts Prevention And Treatment​[/article]