How to stop a dog from licking other dogs pee? He is a boy?

Many dogs do this.
Males will lick where a female dog has urinated.
If he on a lead just pull him away and command him to "leave".
Not much you can do about it if he is running loose though, apart from shooing him away from where the other dog has peed.
Dog parks will the worse places for this behaviour as so many dogs use the park.
Exercise your dog where not many other dogs go.

Keep your dog away from another dog's urine.

That's just what they do. It helps identify where the b itch is in her cycle.

you don't. It is normal behavior for a dog, wild or domestic. I bet he is not neutered. That is the behavior of an unaltered male in many species.

Mind yours

Spray it with water everytime it tries to drink pee