My wife is here on a K1 (single entry). When she gets her AP, how does it work? How is it used?
I'm assuming she doesn't need another Visa pasted in her passport -- she can just travel on her old K1 with the AP Document -- correct???

Please advise. Thanks!

Correct it behaves just like a Green-Card, your Wife travels using passport, and re-enters the country using the AP document.

Thanks! One more question ... on the AP doc, does it say you can come-and-go ONLY to the country you specified on the I-131? Or, is it "generic" (behaving like a Green Card) and can be used to travel in/out from countries other than your native country?

The AP document allows travel anywhere outside the U.S., not just the native country.

But she is still subject to visa requirements to enter the 'other' country - she can come back into USA using the AP but the other countries do not recognize the AP as a US citizenship equivalent document- she doesn't get the same benefits as a greencard holder or a US passport holder.