From your history it is not clear that pus is coming out from scrotal sac or from glans penis
or from penis where urine come out.
Causes,investigations and treatment can be done afterward.
If pus is from scrotal sac and there is itching,is likely infection present with fungal infection
If pus is from glans penis he might have poor local hygiene and there is collection of smegma
and therefoere belano prostitis infection is likely.
If pus is from penile urethra
there may be infection in urine or due to some sexual transmitted disease.
So he should consult sexologist
and seek his advise.