What is meant by the "source" of my assets?

the source of your assets is generally speaking where your tax home was in the year you obtained them.


if you bought an asset while living in the USA in January 2019, move to PR in march 2019 and fulfill year of the move requirements to be a BFR-PR for the entire year, then the source of the assets is actually PR

there are special rules, like the 10-year securities rule, that can overwrite this general assumtion