K2 Veterans Care Act of 2020 This bill establishes a presumption of service-connection for certain diseases becoming manifest in a veteran who served on active duty at Karshi-Khanabad (K2) Air Base in Uzbekistan between January 1, 2001, and December 31, 2005. Specifically, there must be a presumption of service-connection for veterans who manifest illnesses that have a positive association with exposure to jet fuel, volatile organic compounds, high levels of particulate matter, depleted uranium, asbestos, or lead-based paint, as determined by the National Academies of Sciences, Engineering, and Medicine (NASEM). Under a presumption of service-connection, specific conditions diagnosed in certain veterans are presumed to have been caused by the circumstances of their military service. Health care benefits and disability compensation may then be awarded. Veterans who served at K2 Air Base during the specified period are eligible for Department of Veterans Affairs (VA) hospital care, medical services, and nursing home care for an illness that has been determined by NASEM to have a positive association with exposure to jet fuel, volatile organic compounds, high levels of particulate matter, depleted uranium, asbestos, or lead-based paint. The bill also expands the definition of an open burn pit, for purposes of the VA's 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.