What did President Roosevelt know about Pearl Harbor and when did he know it?
FDR did not know about the specific attack on Pearl Harbor. Nobody did. Japan sailed across the pacific under total radio silence to avoid alerting anybody of the attack before it happened. However, he could have suspected an attack somewhere, because he intentionally provoked the Japanese by cutting their oil supply so that we would have a reason to be involved in Europe. A Japanese attack on home turf would be perfect for rallying support for a war with Germany.
To make a very loose comparison, you can compare it to Bush (with no prior knowledge of it) using 9/11 to declare a War on Terror, which basically gives the President the authority to deploy troops anywhere as long as there is terrorist activity (Iraq). (this does not suggest a conspiracy, those theories are retarded)