National Sea Grant College Program Amendments Act of 2020 This bill reauthorizes through FY2024 and revises the National Sea Grant College Program, through which the National Oceanic and Atmospheric Administration (NOAA) supports university-based programs that focus on studying, conserving, and effectively using U.S. coastal resources. Among other things, the bill requires NOAA to award Dean John A. Knauss Marine Policy Fellowships. Currently, NOAA has discretion in awarding such fellowships. The fellowships support the placement of graduate students in fields related to ocean, coastal, and Great Lakes resources in positions with the executive and legislative branches. The bill reauthorizes through FY2024 grants for (1) university research on the biology, prevention, and control of aquatic nonnative species; (2) university research on oyster diseases, oyster restoration, and oyster-related human health risks; (3) university research on the biology, prevention, and forecasting of harmful algal blooms; and (4) fishery extension activities conducted by sea grant colleges or sea grant institutes to enhance existing core program funding. The bill authorizes grants for (1) priority issues identified in the National Sea Grant Program's strategic plan, and (2) university research on sustainable aquaculture techniques and technologies.