These are pretty easy to work on. Just follow the Phillips head screws (or Torx on a late model so built).
It's pretty simple to check for a blockage in the area you've highlighted. Pull the main hose out of the side socket, and it you've got suction at the hose end, the blockage is in the duct in the floor nozzle. If you lack suction at the hose end, the blockage is in the hose. These bagged machines don't offer many other possibilities for blockage.
The duct/short hose in the floor nozzle comes out easily. Remove the single screw holding the lower wand retainer in position, and unscrew it. These are reverse threads. Then you can unscrew the duct/short hose from the fitting in the floor nozzle. Sometimes, a blockage can occur right in the duct fitting next to the brush roll. Something sticky that then attracts other debris and kind of glues itself in place.
One funny object that likes to get caught in the duct/short hose in the floor nozzle is the pull-ring from a plastic milk jug. These can get caught in the coils of the short hose and passing hair and other debris starts to collect. Before you can say Jack Robinson, it's completely blocked.
The hood comes off the floor nozzle pretty easily. Two of the four bottom plate screws hold it in place, then there are two screws up inside the floor nozzle frame that attach, and two tabs, one along each side, that you have to disengage. Once you have the short hose out of the hood hole, it goes pretty easily.
This is a machine that really isn't all that tricky with regard to repair procedures. Just be sure to look at everything, especially under the hood, to make sure you aren't missing a broken part that will cause you to take it all apart a second time. Like the actuator arm on the drive mechanisim. It helps to have this all clean for a really thorough inspection.
When you are reinstalling the floor nozzle hood, be sure to keep the brush roll control knob pushed all the way over to the carpet position. If the screw holes on the hood don't come right up tight to the polycarbonate forward nozzle frame, you don't have it lined up right. There is a tab on the underside of the hood near the carpet height selector that needs to be lined up with a corresponding tab on the p.c. forward nozzle frame for it to fit right. Even if you discover that this is wrong after the screws are reinstalled, you can push it back into place carefully with a flat screwdriver.
One bit of basic advice, be careful reinstalling screws in plastic holes. They won't take much torque and don't need it. If you're unsure, don't use a cordless, do it by hand.
I do this model all the time and it goes very quickly. If they are dirty/dusty beyond what compressed air will blow out, I completely disassemble and wash them out with high pressure water. I have ways of doing it that usually don't require the wiring nor the power switch to be removed. The parts air dry or dry before a wood stove, depending upon weather. I can completely disassemble, inspect, and reassemble one in about 25 minutes. Not counting time to hunt up this or that part. Cleaning/washing time can add 10 to 15 minutes, depending upon how nasty the brushroll is. The motor and drive mech. get blown out/off with comp. air. I clean and repack the b/r bearings which I've got down to a few minutes. Sometimes the cord is bad; that adds a few minutes to replace. I can knock one of these out in under an hour unless I encounter something unusual. Not counting drying time, which makes the process non-continuous. You go do something else while that process is occurring. Like watch a re-run of Gunsmoke or similar.