Final answer:
To modify the font on the 365 login page, you should modify the Azure AD Company Branding Template.
Step-by-step explanation:
The template that you would need to modify in order to change the font of the company name on the 365 login page is the Azure AD Company Branding Template. This template allows you to customize the branding and look of the login page for Office 365. By modifying the template, you can specify the font and other styling options for the company name.