My father is 95 and we are trying to get his gross monthly social security amount to apply for VA benefits for him. How do we find out the amount?

I agree with going online and helping him register and get an account. You should also be able to ascertain how much his Part B costs by reviewing an old receipt or statement from SS. 

Or you should be able to create an online account for him that would give you access to that information. You'd need all of his personal info (SSN, date of birth, etc). Go to ssa.gov 

My dad received a year-end statement.

You should go to a Social Security office near you and ask them directly.