In the example sentence
People today know all about technology use.
Know all is not a verb. Know is the verb here; all is part of the object of the verb.
People today know.
What do they know?
People today know all about technology.
Note that all isn't being added to the verb. It is a modifier of the object. Consider this:
People know about technology.
How much do they know about it?
People know all about technology.
All describes how much they know about technology. It has nothing to do with the verb. Even without the tech bit, I know all is a simple (but valid) sentence with a subject (I), verb (know), and object (all). It could be I know Bobby or I know French or I know a secret and it's all the same: I know [something]. In this case, it's I know [all about technology].
The noun know-all (or know-it-all as is more common around here) is
an informal term because it's a mashup of two (or three) words to describe
someone in a less than flattering way. A formal version (without the
sarcasm that goes along with know-it-all) would be subject matter
expert (or just expert).
So, to sum up, if you want to say people today know all about technology
use, that's perfectly fine in both an informal/conversational or formal
situation. If you want to acknowledge that someone knows what they're
talking about in a more formal setting (without being derogatory), I
wouldn't use know-it-all.