I'm hooked on all the gold shows on Discovery. The "knowing where to dig" is the prospecting part. There seems to be a million little things to look for. Shape of rocks, orientation of the rocks, size of the trees in the area, the shape of the land, how the dirt is packed, etc. I saw a gold show recently where some people bought some land in eastern Oregon and it turned out their whole claim had already been mined out. They were never going to get anything beyond what the old timers missed which was very, very little. They eventually got hooked up with a neighbor who had good ground and no way to get the gold out.
The place I've picked all my 1% of knowledge is
Gold Rush: Mine Rescue with Freddie and Juan. All the other gold shows are about greed and getting as much as possible (which is still fun and I love them). Mine Rescue is about people who are failing at the greed part and struggling hard just to survive. Then Freddie and Juan come in and do what they can to help. They start with a 4-hour test run, then spend a week fixing things, then end with another 4-hour test run to see what effect their changes had. It's a combination of fixing wash plants, setting up wash plants properly and showing people where and how to find the gold. I like that the goal isn't for Freddie and Juan to walk away with gold, but to help struggling miners walk away with some gold. It puts a fun twist on a greedy job.
As for how the old timers found the places to begin with, I'd guess once upon a time someone found gold in a river. Either they saw it just sitting there, or panned out of curiosity. Then they'd just keep working back up the stream towards the source. When the gold runs dry, then you'd be looking for the source of the gold which leads you underground. So the source is where the gold comes out of the earth and is eroded away into rivers and streams. If you're following the source into the mountain, that's hard-rock mining. If you're after the stuff in the rivers and streams, even if they're ancient rivers and streams that dried up thousands of years ago, that's alluvial mining.
I think when "alluvial" is tossed out, it's probably time to stop boring people.

The point is, if you ever get curious enough, Discovery has tons of different gold shows. Gold Rush is the father of them all. So that would be a good jumping off point. But most of the "where to find the gold" and "how to catch the gold" is covered more in the show with Freddie and Juan. Because every episode is new people not finding and catching gold.
One more thing. If you're into metal work and fabrication, Juan drives a semi and hauls his own portable CNC machine around with him. That way they're able to fabricate anything they need on site. If that kind of thing happens to excite you, there's plenty of that as well.