Tessel 2's 5V line is broken out here (yellow box):
The other two holes in the green box let you power Tessel 2 at 5V using wires, e.g. to a battery pack.
If you are planning to use either of those features, I would recommend purchasing and soldering in a 3x1 .1" female header, like this one. This gives you easy, swappable access to those pins.