Summary

USB socket for charging things on your bike via the hub dynamo.
You need a socket like this:
https://www.conrad.de/de/p/usb-einbaubuchse-2-0-180-tc-a-usb-a-top-203-usb-a-1586516-tru-components-inhalt-1-st-1586516.html
and optional a switch like this:
https://www.conrad.de/de/p/tru-components-1pu-kippschalter-250-v-ac-1-x-ein-ein-rastend-2-st-172225.html

Required electronics at least:
Rectifier, Capacitor and LDO
For better electronics look at this:
https://www.thingiverse.com/thing:2810187