I'm looking to purchase a great dane pup, and i was just wondering what sort of questions i should ask the breeder?

This is the ideal, attend a few shows and sort out the type of dog you like, talk to people get a feel for who is a respected breeder and who is not. Make a note of 3 or 4 breeders who have the respect of the rest of the breed owners and ask to visit them, ask about hip scores and health problems, how often do they breed and how long do they think you will need to wait for a puppy. Ask to see the results of the health tests, ask if they will help you join a breed club. Ask the breed club what health tests they advice for breeding stock and at what age a bitch should be bred. When your chosen breeder does mate a bitch ask for the pedigree of both the dam and the stud and research it.