I live near Frankfurt, but I can't tell you much specifics, since I am very seldom directly in Frankfurt.

Milk is around 0.6-1.1€ per liter (which is the usual amount you can buy).

The price of vegetables, fruits etc is very dependent on where you buy it and whether it's organic etc. So I can't give you any hints there.

Sales tax is always already included in the price.

If he doesn't cook for himself I would guess around 10-15€ for food, drinks etc per day. If he can eat at a canteen at e.g. university or does cook it is possibly less.

For buses/subway etc it's best to buy a weekly ticket or similar. He should ask other students what is best to buy as it is dependent on range etc.

Phone numbers are 110 for police and 112 for fire department/ambulance.

For places which he should avoid it's best to ask around other students. He should keep in mind that Frankfurt has around double the people in the daytime than at night, so lots of commuters.

Hope I could help

Cost of living Frankfurt.

Might be a useful guide if it's accurate

@Timmy51m: Thank you!

... I can even found the city i live there...But it's actually cheap than real price because of lack of data.

But i think it will more accurate in other countries.