Watch the credits (which is hard for modern TV, but not so hard for movies). When you see hundreds of people listed under animation and 99% of them have names associated with one culture and that culture's home region is low income, chances are it was outsourced to that region.

It depends on the production. I think this was especially true on US/CA productions while everything was predominantly hand drawn in the 80s/90s. You'd have key-frame animators that laid out the actions, and in betweening would be outsourced. I'm sure it is still done now, especially for TV where the budget is tighter. It's a tricky business, I empathize with owners that want to make the situation better but need to compete on bids, and employees (if that) having difficulty making rent on the frames they can get approved. Like with code, you have to love it to stick with it.

I have no idea what it's like for anime. This is subjective - but I think the quality is usually much higher. I'm not sure how it is done.

If it can be outsourced, it will be outsourced. It an absolute race to the bottom shitshow

For pretty long now. I've been interning in a larger German animation studio in 2003 and while the directors and key animators were sitting on site, I distinctly remember being stunned by the logisitics of the weekly arriving Betamax tapes from Vietnam. All inbetween painting was outsourced back then already.