That looks like the hook for the trailer chains. Why not open the owners manual and see what is written there about the hook?
You can mix dot 3 and dot 4. You will end up essentially with dot 3 but they mix fine. They look exactly the same. I would flush with dot 4. Better to have greater protection.
The only fluid that cannot mix with dot 3 or 4 is dot 5 silicone brake fluid.
I don’t think that is the hook for the safety chain’s as it is right above the hitch there should be two chain hook’s & should be a few inch’s on either side of the hitch.
That is not for towing, it is where the wench is hooked up to pull you onto the flatbed.
That’s the factory recovery hook point. You attach the winch hook from another vehicle to pull you out of whatever you got stuck in off roading. Beware, the factory provided loop isn’t very robust. Nothing nastier that a winch cable that lets loose…
Towing is via the hitch receiver below the loop…