byb and byt , back-yard-trainers , how absurd to recommend an adult Jack Russel Terrier , probably feisty , to sort it out with a 6 week old pup.
The pup was attacked when he got home !
Bad management all round.
"He is a very smart dog but very dominant. This brings me to my other issue, today my partner was fixing a lead into the seat belt so that the dog was put. The dog started growling at him and air snapping. This was definitely agression, he didn't want to be moved"
You got a black dog from a back yard breeder who at minimum should have known that 6 weeks was too early to home , even if you did not.
Who knows other pups might have gone home earlier .
Don't pin any problems on the dog being "working" . Says who? Some sales pitch ? Problems will be due to the byb not having spent the time to properly socialize the pup . What the dog experiences prior to 8 weeks is as important , maybe more so , than what is given after . This is the critical imprint age .
That the pup was that hungry on the ride home shows that the dogs were fed sparingly or in an atmosphere were there was a lot of competition and not enough to go around . Competition for little.
Be on guard for dog aggression problems . Not a good introduction. You are lucky the JRT didn't damage the pup. Not once , twice .
If that were my dog and he didn't want to move , I would put him on lead and he would be moving with me , every where I wanted to go , and quickly , and then I would put him wherever you wanted to put him in the first place. No punishment or time-outs , no bribes . No negotiations.