Final answer:
To modify a project sheet with a dropdown list column, a coworker needs at least the Editor permission level, either 'Editor - can share' or 'Editor - can't share'. A Viewer can only view the sheet, and Admin rights exceed the requirements for just editing.
Step-by-step explanation:
To interact with a project sheet that includes a dropdown list column and perform activities such as editing the data, a coworker would need to have the Editor permission level. Specifically, for Jen's colleague to access and modify the dropdown list, they would need the permission level of Editor - can share or Editor - can't share. The 'Editor - can share' permission would additionally allow them to share the sheet with others if necessary, while the 'Editor - can't share' permission provides editing capabilities without the ability to share the sheet further. A Viewer would only be able to view the sheet and an Admin would have full control over the sheet settings and permissions, which is not required for simply editing a dropdown list.