Observation Details
The asterisk icon to activate a footnote dialog window does not meet minimum target size (24×24px). The icon's target size is 18×21px, making it hard for certain people to reliably click it. This includes people with motor disabilities, people using devices like styluses, people in moving vehicles, and mobile users altogether. Especially considering its use inside other interactive elements.
Remediation Notes
Ensure, making all interactive elements at least 24×24px in size. This does not necessarily mean to make the icon itself 24×24px, if you can ensure a surrounding area of said size to be the clickable area of the icon.
A better approach would however be to not use interactive elements below this minimum size. Also consider mobile users when designing these elements. An increased target size of 44×44px (see success criterion 2.5.5 Target Size (Enhanced) [AAA]) will immensely help mobile users as well.