K2 Veterans Advocacy Act of 2020 This bill requires the Department of Veterans Affairs (VA) to enter into an agreement with the Agency for Toxic Substances and Disease Registry to complete a study to identify and assess any causation or correlation between exposure to toxicants at the Karshi-Khanabad (K2) Air Base in Uzbekistan between October 7, 2001, and November 21, 2005, and incidents of cancer or other diseases in members of the Armed Forces. 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.