Is there any way to get back a dragon that has been sold? I got the wonder dragon from the party island event but my little sister sold it when she hatched the egg for me is there anything that I can do to get it back?

Try sending in a ticket to support and see if they will restore it. In the future you might want to make sure that your sister does not get access to either your game or your device because if you are lucky enough to get it back this will be a one time thing.

@Nynaevelan thank you very much I appreciate your help she has her own dragons account but my dad let her use my phone while I was gone :/