I believe your FE is waived by a particular state board.  So, i would suggest you to take PE in the same state where you got your FE waived.  I highly doubt that your FE will be waived by all state boards.  If you have that liberty, you can take PE from any state you want to provided you have your undergraduate degree from USA.  if you have your undergraduate from outside USA, you might want to evaluate your degree first from CPEES.  some states, however, will allow you to take PE test if you have masters or higher degree from USA even if you dont have undergrad from here.  regarding PE exam schedule, i believe it is already too late for April, so you might want to try for October.  good luck