Patients who are taking treatment for schizophrenia can drink alcohol.
If yes how much quantity per day or week. If no, what happens if they
drink occassionally say once in a week.

I'm not doctor but I take medication for such disease. I must say that
I drink a lot but I should not because:

if you take antipsycotic drugs like Zyprexa, drinking will make you
very tired, and not enjoy the buzz (and that's what I need). Drinking
can lead to more paranoia (in my case).

if you add drugs like benzodiazepines the liver will have a hard work
"digesting the combo".

But hey, I'm still alive so I think drinking is not a big problem if
it's a mild schizophrenia.

DIY: read all the medication documents then decide.

I think the better answer is pick up the phone and talk to a doctor
about the medication the patient is receiving and ask about alcohol.

Thanks for the reply