Why would you think you know the correct answers?
1. Several breeds have spinal problems - most of the dogs with elongated backs and short legs tend to but also GSDs and several other breeds can have issues with spinal stenosis and other issues. I have known several Dobermans with spinal problems as well and several Schnauzers. I have known mutts with serious spinal issues as well.
2. The average age depends upon the breed but usually 8 yrs for the larger breeds to the late teens and early twenties for some of the toys. I have known Dobermans that have reached 19 and toy Poodles that died of natural causes at two years. So there really IS no 'average age'.
3. It would likely be a runt of one of the toy breeds or mixes of toy breeds. The supposed 'smallest' BREED of dogs is the Chihuahua but I have known runt Yorkies smaller than average Chihuahuas so again, not an absolute in the answer.
4. There are Irish Wolfhounds that have brown and black in their coat but it would depend upon what you are considering 'largest' - largest in size at whithers or weight... but most breeds can have brown and black hairs in their coat. Doberman Pinschers are not intended to be large dogs at all - they are supposed to be a medium sized breed with b*tches 25.5 inches at the whithers and dogs 27.5 or so inches at the whithers.
5. The most 'popular' breed registered with the AKC is singularly the Labrador and variety-wise the Poodle (since they come in three varieties the cumulative statistics would make them the most 'popular' registered dogs. The real 'most popular' is likely the mutts or mixed breeds as people tend to allow them to just breed indescrimenently and there is a fallicy about them being healthier and better tempered but again, a falsehood but people as a whole are ignorant of dogs so they believe that nonsense.
6. Many breeds were utilized for 'fighting' 'back then' - whenever the heck that is supposed to be! hahaha
7. Xoloitzcuintle, Aidi, Austrian Pinscher, Caucasian Ovtcharka, Central Asian Ovtcharka, ESTRELA MOUNTAIN DOG, etc. many, many....
8. A dog (which is the term for male canine) is neutered, not spayed.
9. That is an ambiguous and impossible to accurately answer since many of the facilities in the world do not send in statistics. A sufficient number so that millions of companion animals are destroyed annually in the USA alone.
10. There again is no accurate answer to that question as it is not a reportable or accurately studied statistic. There are often reported statistics but they are erroneously based and mere guesses but suffice it to say, there are a paltry few that are adopted when there are so many that die on the streets and in shelters and in back yards.