Temp Probe with Brisket

Stick your probe in from the side of the flat part of the brisket.  As close to the midway point as possible from the side.  You might also try poking the brisket with a toothpick in a number of locations on the flat, if it slides in with little resistance, it's done.  Some reach that point at 190, some not until 210.  I usually shoot for 205, but go by the toothpick test to know for sure if it's done.