Domestic Terrorism Prevention Act of 2021 This bill establishes new requirements to expand the availability of information on domestic terrorism, as well as the relationship between domestic terrorism and hate crimes. It authorizes domestic terrorism components within the Department of Homeland Security (DHS), the Department of Justice (DOJ), and the Federal Bureau of Investigation (FBI) to monitor, analyze, investigate, and prosecute domestic terrorism. The domestic terrorism components of DHS, DOJ, and the FBI must jointly report on domestic terrorism, including white-supremacist-related incidents or attempted incidents. DHS, DOJ, and the FBI must review the anti-terrorism training and resource programs of their agencies that are provided to federal, state, local, and tribal law enforcement agencies. It creates an interagency task force to analyze and combat white supremacist and neo-Nazi infiltration of the uniformed services and federal law enforcement agencies. Finally, it directs the FBI to assign a special agent or hate crimes liaison to each field office to investigate hate crimes incidents with a nexus to domestic terrorism.