What is the code po447. And how y Fox. Pathfinder 2008 v6. Thanks

There is no easy answer for how to fix it without a thorough diagnosis or the EVAP system to determine the cause that is triggering the fault code. The car's PCM runs a diagnostic test to check the condition of the EVAP system and throws this diagnostic fault code, turning on the check engine light, to flag an EVAP system problem with one or more of the numerous possible causes which include the possibilities of:
Faulty or loose fuel cap
Faulty purge control solenoid
Charcoal canister clogged or broken
Fuel vapor hoses cracked or broken
Vacuum lines cracked or broken
Faulty pressure sensor
Faulty flow sensor
Test each possible component to isolate the cause(s) and then fix or replace the faulty component.
Here's a great tutorial video, I just viewed yesterday, that will help you better understand and diagnose an EVAP system.
https://www.youtube.com/watch?v=LYifnstYsx4

That's gotta be one of the worst codes these things can throw. A true PITA.
You can throw a pile of money at the problem and still not be guaranteed that it's fixed.
My 2002 has had that code for years (check engine light on), and I refuse to spend money chasing ghosts.
My trusted mechanic told me years ago that unless I'm selling the truck and need it to pass an inspection, just leave it alone.
It doesn't affect how the vehicle runs in any way.
Chances are now, after 18 years of ownership, I'm just going to continue driving it until it breaks, and then junk it.
For me it's not worth spending any money on to try and eliminate this code.
Your situation is probably different, but that's where I'm at.
Cheers.

This kind of problem is most easily diagnosed with a smoke test. I recommended a friend of mine to have a mechanic do a smoke test for $120. They told her exactly where the problem was - on an older Forester it was the vent valve and solenoid valve. I replaced the two parts for her and no more check engine light.