As per his force abilities, Freedon Nadd was of course an expert in sith sorcery seeing as how he was the main source of Darth Zannah and Exar Kun's knowledge. As such it's very likely he knew the dark tendril power, illusions, and the force blast power. He was also likely skilled in drain given the ritual Kun performed. His telekinesis as a spirit was such that he could tool Kun (although before his prime) as a spirit so it's likely he wielded highly advanced telekinesis. He also of course knew techniques to keep the orbalisks out of your face and hands.
As per his fighting style, given that he was force specced, he likely used Niman for it's relaxed practice requirements and chaining in force attacks, or Soresu for it's defensive capabilities allowing him to gather energy for force attacks while defending against opponents in a saber duel. It's also likely that given the nature of his orbalisk armor that he utilized Djem So to take advantage of his physical capabilities and near impervious armor. It's also likely that given his habit of wielding a blaster in combat and thus range fighting that he used Shien to deflect his opponents blaster shots. Any of these seem like they'd fit Freedon Nadd
Freedon Nadd was known to wield a bronze shoto and his own personal blaster which I assume was imbued with some kind of dark side energy. He also had his orbalisk armor and may have made use of force increasing artifacts.
This is what I have for Freedon Nadd so far.