You do not need to over-think this. I have owned several breeding jacks (standard and mammoth) and raised mules for many years.
They learn from punishment (negative reinforcement) just like horses only they learn quickly from it -- usually more quickly the most horses.
The one thing you have to really think about before you punish one is if you have enough control on the lead-rope so that the donkey does not pull away from you. They are probably 3 to 4 time stronger in the neck than any horse. If they are not tied or you do not have a chain on one, IT WILL pull away. Then, you have taught it a bad habit instead of correcting one.
This Donk needs to be punished -- plain and simple -- when he kicks. He will quit and will not do it again if you punish him severely enough the first time, there will not be a second time.
If he were mine, I would 'set him up'. I would tie him with a regular lead on a nylon web halter. I would also have a second lead on him that I handled. I would use a chain -- probably under his chin. [I would let him tell me how tough he thought he was.] If he thinks he is tough (bared his teeth or lays his ears back), I would probably just go right to the chain under his upper lip.
Then, I would take a cattle sorting stick (5 foot long fiberglass pole that stockmen use to sort cattle) and touch him on the back or hip. When he kicks at it (and he will) I would just go to work on him with the chain giving him several really hard jerks. I would leave for a few minutes and go back and do it again. You have a 50/50 chance that there won't be a second kick. If there is, jerk harder and more times.
When he is ok with being touched while tied, I would go to the same thing while leading him. Do not do this without leading him with the chain. He WILL jerk away if you do.
He should learn manners just like any horse. Aggressive behavior needs to be met with punishment, plain and simple. It is not rocket science. These animals can and will hurt people and can kill people. You do not ever want a donkey to bite you. They do not miss like they do not miss when they kick. A donkey that bites is as different from a horse as a bulldog is from a collie. Their mouth opens wider and closes with much more force. So, keep in mind that if you do not punish him severely enough to make him mind, you will just make him mad and he will bite -- hard.
Every Jack I have ever owned was just like a big puppy dog. They did not all start out that way. But trust me; they discipline just like a horse. When they are nice, they are nicer than a horse and much more affectionate. After you make him mind, he will get very friendly and very affectionate.