While I myself have never worked for a big chain I've been in the trade long enough to know a bunch of people who have. Almost invariably the duration of their employment with said chain is inversely proportional to their concern for the individual animal and amount of knowledge on their care.
Wow my Petsmart NEVER did any training of that sort. It was watch some Petsmart Introduction video and BOOM you are right on the floor selling fish. I only learned from the other associates how to do the chores morning and night. But never learned any information about any of the pets needed in pet care. Though my knowledge I solely learned is primarily on fish/small animals/birds I was lost on reptiles.
As for applying for the job, my Petsmart only want employment via online. You can always call in and ask what they are missing and apply for that spot.