1)
Why does it say "Kevuras Chamor Yikaver"?
1.
Rashi (Divrei ha'Yamim II, 36:6, citing Targum Yonasan): Just like a donkey's carcass is carried, his body will be carried. Radak - a donkey's carcass is not buried; it is carried and cast to the wasteheap. So Yehoyakim's body will be cast outside the gates of Yerushalayim. He died outside Yerushalayim when they were carrying him to Bavel the second time, and they did not let him be buried.
2.
'Rashi' (Divrei ha'Yamim II, 36:6, from Vayikra Rabah 19:6): His 'burial' was like a donkey's, in a dog's stomach.