Reference Book: Star Wars Saga Edition Knights of the Old Republic Campaign Guide
Sonic damage is considered to be Energy damage in all ways. However, ranged weapons that deal Sonic damage cannot be deflected by a Lightsaber. If a weapon deals bonus Sonic damage (such as those with certain Gear Templates) in addition to its normal damage and is not purely an Energy attack, the attack can be deflected by a Lightsaber, but the target still takes the Sonic damage regardless (just not the weapon's normal Energy damage) if the attack would normally hit.