K2 Veterans Toxic Exposure Accountability Act of 2020 This bill addresses the exposure of members of the Armed Forces to toxic substances at Karshi-Khanabad (K2) Air Base in Uzbekistan between October 1, 2001, and December 31, 2005. Specifically, the bill requires the Department of Defense (DOD) to study and report on the exposure of members of the Armed Forces to toxic substances at K2 Air Base during the specified period. The bill also expands the definition of an open burn pit, for purposes of the Department of Veterans Affairs (VA) open burn pit registry, to include burn pits located on land in Uzbekistan. A burn pit is an area used for burning solid waste in open air without equipment. DOD and the VA must ensure that individuals deployed to K2 Air Base during the specified time period are covered by the Depleted Uranium Follow-Up Programs of the departments. Such programs study the health effects of depleted uranium exposure and provide treatment. Upon request by the National Academies of Sciences, Engineering, and Medicine, DOD and the VA must provide information for the performance of a study on the exposure of humans to toxic substances at K2 Air Base during the specified period.