How to connect a TVS to protect the data lines in a USB device port?
This style of TVS is intended to be either connected to a power rail, or to be connected to ground only. In that second mode, a positive transient pulse will go through the top-side diode, then break down the TVS diode around 6V, clamping to ground through that device.

Here is a datasheet from Semtech that describes how to use one of their parts like this. See Figure 4 on page 7.

tl;dr, they connect the common cathode to \$V_{bus}\$, which is +5V.

This additionally serves as ESD protection for \$V_{bus}\$.