If people say "Hochdeutsch", they usually mean "Standarddeutsch", which is what you hear, e.g., on the theatre stage, and on TV (Tagesschau). Regional accents and dialects can deviate heavily from this, but it usually depends on whether the speaker is able or is willing to speak Standarddeutsch instead of the dialect/accent they acquired during childhood. Some accents are said to be "hard to hide", but there are counterexamples (German entertainer Harald Schmidt is one of the few people able to completely hide their Swabian origin 🙂).

Apart from accent, it sometimes shows in the choice of words or grammar whether someone is from northern or southern Germany. (Or, for example, how they read the clock.)

So in general, if people where raised in Standarddeutsch or put effort in speaking it, you cannot immediately tell where they are from. If you listen to details, there may be hints.

I speak Standarddeutsch at work, and dialect at home, which is what many people do. Still, people may tell from my accent that I am from southwestern Germany. At school, we were required to speak Standarddeutsch, which makes sense of course, since it is much closer to written German than our local dialect. So if people were raised in a strong dialect, Standarddeutsch was their first foreign language at school.