Where to solder on for sandisk thumb drive to recover data

I don't think the six holes will offer what you want.

If you look at the USB plug attachment part of the PCB (left side) where it's broken you can trace the lines to the chip which are not wired to the holes as there is no via's to jump to the other side (likely a two layer board). I would use a meter to check continuity where the solder joints are on the chip and the severed lines where the board snapped to find the needed lines.

Do you know which version of USB this thumb drive offered? As that gets into how many lines need to be connected. Here's a good reference USB Pinout, Wiring and How It Works

Then repeating the same task on the broken plug piece you should be able to identify which line goes to which pin of the plug. Then using an old USB cable of the same rev of USB soldering on the tails to the board as needed.