The measures that have been suggested are all (well,mostly) fairly successful to try with *horses*.
*Donkeys* however can be a rather different kettle of fish. I don't know what the situation is with this donkey -- if the o.p. has not *tried* yet to train him to be (properly and coordinated-ly) paste-wormed, or tried hiding powder in molasses and grain, or using a wormer bit (which IME work poorly with ponies) or hiding wormer in applesauce, then those things are certainly worth trying, and might well work.
However there are some donkeys in this world that just Will Not Permit the taste of wormer to pass their lips and can get pretty ornery about it too. The applesauce-in-a-syringe switcheroo will always work the first time but I know one animal who will never, ever let anyone else near his mouth with a syringe of *anything* again
Donkeys can be particularly adamant and agile and they kick rather hard when perturbed.
If this is the o.p.'s situation, the best bet would be to either see if you can get the donk to eat daily wormer pellets; or try REAL HARD to train him to eat applesauce, and then give him a large enough quantity with the wormer in it that it is not really taste-able; or if all else fails a vet can sedate and tube him.
Donkey brains really do not work like horse brains, and they are a much more formidable and stubborn opponent if they are not on the same page as your program
Good luck, have fun,
Pat