Donaldson may or may not be tradeable because of his contract and injury concerns, but I would wait until the off-season to look into trading him. He is currently sidelined with a nagging injury and that will be fresh on teams minds when discussing returns.
What I would look into doing is something like this; Trade Simmons, he is a plus defender and should bring a decent prospect. An infield of Kirilloff, Arraez, Polanco and Donaldson would be in place for the rest of the year. IF Miranda continues his hot AAA start, bring him up to be the utility guy, he has played all infield positions in the minors this year. Keep Gordon up as another utility guy, he has played passable defense at 2B & CF. A Cruz trade or Sano trade/release are subjects for another topic.