Earl another donk of ours, grabs on to anyones clothes if they come close enough to his stall, and will just HOLD you there until you give ONLY him attention, then he lets go. He has never bitten anyone, just a bad habit he has of grabbing the clothes! YEs, donks can bite..especially jacks, and you should ALWAYS be especially careful when breeding.
My baby donkey bites me all the time playfully. I am trying to break her of that without discouraging her palyfulness. My jack is laid back and has never bit anyone. He is a gem. He has bit the quarter horse plenty. His is attemping just that in my avatar.