I love my dog. Dogs were the first species to be domesticated.
Is your dog friendly?  Are most dogs friendly?
Yes very friendly. Their association with humans have made dogs very attuned to human behavior.
I wonder why other similar animals like wolves can't be domesticated?
There is Intra hybridization among wolves and dogs because their species are so similar, and genetically very close. 
If you cross a dog with a wolf, will the offspring be domesticated naturally?
Not sure. but such hybridization has been detected in many populations in Europe and North America. 
Perhaps the hybrids are a good thing so the species does not decline thru inbreeding.
Although that may impose certain evolutionary costs inbreeding avoidance limits the number of potential mates
Good point. I hate professional dog breeders who ruin health of dogs by breeding them to look a certain way.