The German U20 forward originally joined Everton's Under-23s on loan in January, hoping to earn a permanent transfer to the Blues but his spell was cut short by injury.
He is now back at Finch Farm after a second loan was agreed with his parent club that will keep him on Merseyside until January next year.
“I'm very happy to be back,” Donkor told evertonfc.com. “I'm looking forward to pre-season to show my teammates and the fans that it was the right decision for the Club to re-sign me. I'm very proud to be here and I want to show my best performances.
“I started very well here last season but the ankle injury was a big disappointment. I was out for about eight weeks and I had to go back to Germany and do all my treatment. But I got fit again quickly and now I'm feeling better than before. I'm feeling at 100 per cent.”