There are some fonts that are visible in kde's font management application that I can't find on my system.
Here's what was already tried: https://forum.manjaro.org/t/location-of-fonts/148996/6

Since fonts can be use system wide (for all users), they need to be in a system wide folder: /usr/share/fonts
But I strongly suggest you do not modify anything in there

The fonts are installed as System Fonts but some of the fonts that are visible in Kde Font Management aren't in /usr/share/fonts .

Operating System: Manjaro Linux
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.15.0
Kernel Version: 4.19.126-1-MANJARO
OS Type: 64-bit
Processors: 2 × Intel® Celeron® CPU G465 @ 1.90GHz
Memory: 15,6 GiB of RAM

which fonts are you talking about?

Just for example: "Aachen"

But there are more.

Hm, I don't have that one, using just the standard set that comes with my distribution.

Keep in mind that additionally installed fonts can be stored in /opt/, it all depends on how the individual distribution handles user made addons. Also some fonts are not in individual files but are part of bundles

Is there anyway to reveal a font's location in Kde Font Management?

If you hover with the mouse on a font, the tooltip shows you the paths

I hovered with my mouse cursor over the font but I didn't get any tooltip

maybe because the tooltips are not activated by default in your distro?
System Settings -> Workspace -> Workspace Behavior -> Visual Behavior: Display information tooltip on mouse hover

The Display information tooltip on mouse hover box is checked.

Try this: on the upper right, set the filter criteria to "File Location", then hover over the font and wait 2 seconds.

User account-specific fonts might also be found in ~/.fonts

ok that worked. Thanks