(1) Background: A significant proportion of cancer survivors report experiencing a cognitive fog that affects their ability to think coherently and quickly, and reason with clarity. This has been referred to as cancer-related cognitive impairment (CRCI). CRCI has extensive impacts on the daily lives of people living with or beyond cancer, including occupational, social, and psychological functioning. Oncology health professionals report feeling under-resourced to effectively assess the needs of an individual with CRCI and then provide optimal care and referral. (2) Methods: The objective of this project is to develop and provide an initial validation of the first purpose-built unmet needs assessment for CRCI: the Unmet Needs Assessment of Cancer-Related Cognitive Impairment Impact (COG-IMPACT). We will use a multiple-stage, co-design, mixed-methods approach to develop and provide an initial validation of the COG-IMPACT. (3) Results: The primary anticipated result of this research is the production of the COG-IMPACT, the first purpose-built unmet needs assessment for CRCI. The assessment could be used by health professionals to understand the unmet needs and facilitate optimal care and referral for cancer survivors, by survivors to elucidate their supportive needs and advocate for their care, and by researchers to examine the correlates of unmet needs relating to CRCI, as well as how best to support people with CRCI.