How can I measure TVS diode for Seagate Momentus 7200.3?
According to the link to the SATA pinout of the forum page you linked to, pins 7,8,9 are all +5V, so that is just for one end of the diode. Presumably the other end is connected to pins 4/5/6 or 10/11/12 and you could replace it with a TVS diode of the same physical size and a rated voltage above 5V. Given that 5V ICs usually work at least 0.5V above or below the 5V spec, and the 5% tolerance of the TVS threshold, you should be safe with a 6.8V TVS diode. They are usually unipolar so getting it the right way round is important (otherwise you are reducing the 5V rail to 0.7V).

You can't measure the breakdown voltage of a TVS diode or zener using the resistance range of a meter. They are deliberately non-linear devices, so the resistance you measure depends on the voltage applied. The only way to measure the breakdown voltage with a meter would be to isolate the (working!) device, use a current limited adjustable voltage supply set to 1mA, increase the voltage until 1mA flows, then measure the voltage across the device. For smaller devices rated less than 5 watts, you probably need to use the pulsed version of this method to avoid heating the device up too much.