Can someone tell me where the on-the-fly font viewer and selector is hidden?
Scribus does not have this functionality. However, there is a script which will create a document displaying all your installed fonts, which can be printed if you want a hard copy. You can use this as a reference.
You will also find that word processors do have the option to display fonts in the selection box, so that is what I would recommend. Scribus is a layout program, not a word processor. The idea is that you create graphics in drawing and paint programs, text in a word processor, and assemble them in Scribus.
You didn't say what version of Scribus you are using or what your operating system is. Sometimes that is useful information for troubleshooting, so please include it in future posts. And, although it will not add the functionality you desire, I would recommend 1.4.0 RC5, which is still just a "Release Candidate" but is what most everyone is using now for production. It is very close to release.