The antenna feed point is the point where the Coax connects to the antenna in this case that would be where the Pl 259 screws into the snug little hole on the SO 239 at the bottom. The RF choke should be as close to the feed point as possible adn it don't hurt to slap a couple of Ferrite’s on the line just below it. A good choke uses 25' of Coax wrapped on a piece of 6" Dia PVC drain pipe. A small Folgers Plastic coffee container is perfect size. Don't use Metal!