Apple, tech companies to bring back $400B in overseas cash to the US
cnbc.com
cnbc.com
Most of this money is invested abroad already.
Most of the money will probably just sit still in a wide variety of investments (bonds and other stuff; Apple is one of the biggest players in these markets); the rest will go into dividends and share buybacks. A symbolic percentage might go into R&D and Trump will tweet about it.
(I might be wrong, but that is what I expect.)