What's the fuel consumption for Honda FTR223 2007?

It all depends on how you ride, the bikes milage, how its serviced.

Way back 55 years ago Honda advertised their little 50cc Cub at over 100 miles per gallon,  I never got over 60.

Mileage, care. Those estimates  Are  estimates, and ridden conservatively.

 Has the rear tire been changed to a smaller profile?

My Harley  once got 50 MPG, but it quickly drops to 48 and even 30 on hard throttle and in the city. My old Honda got 52 consistently. but dropped to 48 on a lower profile tire.

2007. Its not new anymore. Wear on the engines internals is going to effect its overall performance. Not to mention riding it faster under harder throttle uses more fuel. New tires and chain and a tune up will perhaps help. Its old . Ride it till the wheels fall off. 

Give the bike a tune-up.  It might consume 20% more after.

"which part is wrong"

The knob on the saddle.

FUEL ECONOMY ESTIMATES ARE BASED ON DRIVING UNDER  90 KPH,  so yes, driving fast or at high rpm reduces the fuel economy drastically. Duhhhh.

What could it be? Lessee... tires, sprockets, chain, ignition, valves, blowby, wear on gears, et cetera. Spruce 'er up with a new chain and front and rear sprockets--but not made of spruce. Check 'er compression and 'er leakdown, give 'er a nice valve adjustment, check 'er timing, make sure you gitcha an accu-rite tire (pronounced "tahr") gauge to keep dem donuts nice an' round, and if you wanna you can check fur dem hydrocarbon emissions. Oh yeh, check dem wheel bearings and dem swing arm bearings. Lubricationalize whut dun need lubricationalization. Adjust the idle, etc. Thet motorcycle warn't tuned permanent-like at the factory, so she dun need tuning. Concert A's 440 Hertz, dude.

DUDE... the bike is 14 years old!

Imagine, a 14 year old bike does not have the same gas mileage as when it was driven out of the dealership brand new. SHOCKER!!!!

There might be something that you can have repaired that will improve the gas mileage.  But it's unlikely you are every going to get the same mileage it got when it was brand new.