While I understand everyone's concern about Dante's age, I do not understand why the owner appears to be taking the heat for something that is the breeders responsibility; no matter how subtley it is said - it is being said to the wrong person. Let's just be thankful that the owner is a) someone who is interested in doing the right thing and asking questions and b) a vet student who should be able to offer lots of appropriate care to Dante as he grows.
I do not agree that 6 weeks is too young to start training. What do we think pups are doing with mom and sibs if not teaching and learning themselves? While 6 weeks is too young to have ANY expectations they unequivocally know a behavior, it is never to early to start working with puppies. Each of my litters are introduced to all sorts of behaviors and cues the minute their eyes and ears are open. Mine are all quite proficient actually by 7 weeks at sitting AND waiting as a group for their supper as has been shown in the pictures I have used in articles and adverts.
While I think Dante's owner is on the right track with regard to teaching Dante tricks and manners, et al, I do also hope that s/he is putting as much effort into Dante's socializing. This is CRUCIAL since Dante has been seperated from his mom and sibs so young. It is IMPERATIVE that Dante meet and greet and play with other friendly dogs and puppies between now and at least 16 weeks of age - dogs/pups are able to teach them things humans can not replicate. Note: They can not be the same core group of dogs and puppies - because the core group then becomes the "pack" and you start to lose the pupose and benefits of true socializing. Same goes for people. Dante needs to meet and greet young people, old people, fat people, skinny people, disabled people, black people, white people, green people, people with hats, moutaches, beards, etc. You can not OVER socialize as long as you do it correctly and it is all in FUN with lots of food; nothing ever scary and nothing ever forced. If Dante does not want to approach the man in the funny hat - do not make him - you will instill life long fear of men in funny hats. Instead have the man get down to Dante's level, have lots of food and encourage Dante to approach at his own speed. You can even throw food towards the man and have Dante approach but tell the man to NOT interact in any way with Dante upon his approach - just the approach is enough.
But I regress (Dante's person if you want a copy of my very verbose puppy packet that I hand out at my puppy classes - email me privately firstname.lastname@example.org and I will send). So - how to teach the pup to "growl" on command. First you have to teach the pup what a marker cue is (such as the clicker or a verbal (and excited) yes!). To do that you click and treat or say yes! and treat multiple times throughout the day for several days - Dante does not have to be doing anything - just standing there while you click/treat yes/treat. Some folks likes to put their pups on leash, then stand on the leash while they do this so the pup can not run off.
Once he knows what the marker is then you can start finding behaviors you want to mark. In this instance the "growl". I assume you have heard the noise before - at 6 weeks I can well imagine that what you are hearing or what you like is when he grrrrs at you in delight or play vs. actual growling at you to tell you to "piss off" - there is a big difference to the intent. Grrrs in fun are rather cute esp. when they kind of stretch their necks up to make it happen - almost a prelude to a chortle. Since, as I said, I assume you have heard this noise before - you will need to think about what brought the noise on to begin with then try and duplicate it. (That said - IF Dante is truly growling to tell you to piss off as he would to a littermate - I would perhaps not mark that but try to encourage him to make happy, playful noises as the last thing you will want is a pushy puppy who thinks you are a sib he can push around.) The minute he makes a happy peep - any peep I would click/treat for the noise and continue to do whatever it is that encourages him to make the noise click/treating for each peep. If at any time he offers it without your encouragement - jackpot him - jackpot to mean many small, successive, treats being fed to him rapidily NOT just a handful for him to chow on. Note: you can also say good "growl or speak" or whatever your cue word will ultimately be as you reward so the word is starting to become associated with the behavior. NOTE - do not ask for the behavior via the cue word in the beginning - you will only teach him to ignore the word. Only pair the word with the food reward AFTER he has offered it. Sequence would be: growl -> click/"good speak" at the same time the treat is given. NOT "Dante speak….Dante speak....Dante speak" while frustration mounts because he is not giving you what you want.
Once he begins offering it more often (ie he is "getting" the idea of what you are wanting and he is getting rewarded for) then you can start to ask him to offer it - but only once. "Dante speak" - if he offers you ANYTHING that remotely looks or sounds like he is speaking or trying to speak - REWARD. If he does not, ignore, do something else then come back to it knowing he is not quite ready to have the cue asked of him. Do not repeat the cue over and over and do not settle - just go on to something else and come back.
I hope this helps. I have had two basenjis that speak on command and it is a fun trick since most people still think basenjis are mute and are amazed they can make "dog noises."