Can this machine handle a King size comforter?

Yes, but it won't properly or thoroughly clean it as this washer DOES NOT provide a sufficient water level to do so.

Hi -., for this 4.3-cu ft High Efficiency Top-Load Washer, we would recommend using the "Bulky/Sheets" cycle to wash large items such as jackets and small comforters. The washer will fill with enough water to wet down the load before the wash portion of the cycle begins, and uses a higher water level than other cycles.