Probably to check for phimiosis? Something like 95% of uncircumcised boys can retract their foreskin by the time they're 10, so if a 12 year old can't then it's likely he has some sort of issue. She also said that the NP discussed foreskin hygiene with him, which makes it seem like her son might have had some build-up under there, so they're probably checking for cleanliness too.