How can i transfer this to my other ipod?

so i have this ipod and the memory is all full so my dad gave me his empty 16gb one and i have tried to transfer all my music to my new one and i cant! all of the music on my ipod is not in my itunes library so is there any way i can put it in my library or something? i just want all my music from my old ipod on the new one, thanks for the help its appreciated.