I need advice on wall repair?

If it's just a dent in the dry wall I'd spackle it, let it dry, then get a square piece of wood large enough to cover the entire dent and screw it in place, then paint it. Done.

This will give the door knob something to hit without damaging the wall again.

You can buy a part at the hardware store that is made for this repair. You attach it to the wall over the dent and it will act as a bumper in the future. It is about 5 inches in diameter, so it covers up the past really well. Kind of like a modern politician...

Buy some drywall compound (mud) from a home improvement store in a small container. Using a kitchen spatula with no holes in it, fill the dent to flush and scrape off excess. Use a wet rag to wipe the mud from the surrounding surface and wipe a bit off the patch. Let dry for a day or two until uniform color. Fill the cracks with more mud and match texture with a sponge or cloth or spray texture..

If it's just dented, you can fill it with spackle, sand it and repaint. It may take two applications of spackle. It's much easier if you have a putty knife wider than the dent.

While the spackle is drying, install a doorstop at the baseboard, or one that goes on a hinge pin, so this doesn't happen again.

Use Aluminium Mesh for Fast Drywall Repair.

Fix Cracks for dry wall repair.

Fix Popped Drywall Nails and Screws.

Heres a quik fix go to hardware store buy a round do knob stopper thats bigger then the dent .stick it on wall .

Patch it with a few layers of Durabond 20.