> What are the minimum fonts required for Fedora 28/29 with en_US locale?

Please ask a better question.

It depends on which subset of Fedora (Workstation using GNOME,
Server, Minimal, etc.) and what data you ask it to process.
Some servers which run Fedora never render any fonts at all.
Or, under Fedora Workstation using GNOME desktop environment,
then you might try to view a web page, or print a .pdf file
to an attached non-Postscript printer, that could "require"
an arbitrary font regardless of locale.

Here's how to get one useful answer: Download Fedora Workstation Live,
boot it from a USB flash memory drive (or in a Virtual Machine, etc.),
login and run
     rpm -ql $(rpm -qa  |  grep font);
in a Terminal session.