A group of donkeys is commonly referred to as a herd. Donkeys are social animals and often live in groups, especially in the wild or on farms. The term ‘herd’ is used to describe a collection of these animals when they are together.
In some contexts, you might also hear the term drove being used to describe a group of donkeys. This term is less common but still correct. Both ‘herd’ and ‘drove’ are acceptable when referring to a group of donkeys.