It is worth as much as 60$ to 120$.
Face value only.
Regardless of the Federal Reserve District that distributed the bill, as of 09/2012 a 1928 $100 FRN retails for $125 to $180 depending on condition.
Your bill was distributed by the Federal Reserve Bank of San Francisco but like all US bills at that time, it was printed in Washington DC. Please see the Related Question for details about prices and conditions.
If circulated, $65 to $95 depending on condition. Uncirculated, around $300.
To clear things up, the bill was distributed through the San Francisco Federal Reserve District. There's no agency called the "San Francisco Reserve". In addition at that time all bills were printed in Washington. Different sets were (and still are) printed for each Federal Reserve District as demand warrants but there aren't separate printing facilities for each one.There's more information about its value at the Related Question.
It's still worth one dollar.
A denomination is needed. Please look for questions in the form "What is the value of a 1928 A US [denomination] dollar Federal Reserve Note?" for specific information.
I don't know but I have one too and I am interested to know.
Please see the question "What is the value of an 1899 US 2 dollar silver certificate?"The Federal Reserve System wasn't established until 1914.Silver certificates were issued directly by the Treasury and weren't connected to the Federal Reserve Bank.
"A" is the highest series letter for 1928 $50 Federal Reserve Notes. You may be looking at the Federal Reserve District letter instead - please see the question "What is the value of a 1928 US 50 dollar Federal Reserve Note?" for more information.