A Confessor is more of template then a class. It's just simply too powerful for something like a class. Now, if they just want to make a character that manipulates the minds of others, then yeah, Psionics (Telepathy) or Enchantment specialization is the way to go. Thrallherd is pretty much that exclusively.
Though my recommendation would make a template instead, adjusting its powers to your liking, then having them quest for it to achieve a ritual to add the template (the original confessors were made, not born, though the power was passed on to descendants.) And then give it an ECL of course for balancing purposes.
As a non-OP (for a confessor) example.
Confessor (Template) -
ECL +4 for Females (+8 for Males)
+4 charisma, +6 Diplomacy, +6 intemidate
Confessor's Touch - spell like ability (As dominate creature except as follows, (Requires a melee touch attack, automatically succeeds when grappling or being held by a creature)) DC 5 + 1/2 character level + Cha mod, duration is 1 day per point of charisma mod. Can only be removed by break enchantment (if the caster is equal or higher caster level), Wish, Miracle, cannot be cancelled prematurely except in case below. Caster level is equal to total hitdice. This ability is a free action. Male confessors can use the ability at will. Female confessors require at least one day of rest between uses (reduced by 2 hours per point of Con bonus to a minimum of 1 hour), takes subdual damage equal to 1/4 of their hp rounded up, and become fatigued until they've received at least 1 hour of rest. This penalty only applies on a successful use of the power, but it does require one turn before a new attempt can be made. Male confessors must only wait 3 rounds before re-attempting Confessor's touch. One creature per point of Charisma mod can be dominated at once. If a domination would put the caster over their limit, the oldest domination is released.
If surprised or otherwise suddenly distracted, requires a DC 20 concentration check to avoid casting the ability. Only applies if being directly touched when this occurs.
Con'dar - 1/day. Requires a character level of 16 or higher. DC 35 Concentration check to enter Con'dar (Requires a full round action, doesn't use up the attempt on failure). During this state the normal penalties and usages restrictions for Confessor's touch are suspended (though penalties in effect (fatigue, subdual damage) still apply), and the DC is changed to 10 + Character level + cha mod. As a standard action the confessor can use Confessor's touch as a ranged touch attack with a 20 ft range. Once per 3 rounds as a standard action the Confessor can fire a bolt of negative energy dealing 1d8 per 2 caster levels (cl=HD). This is a ranged touch attack with a range of 20 Ft. Con'dar lasts a maximum of one round per point of constitution, but any damage suffered requires a concentration check of 20 + damage or the effect ends prematurely. At the end of Con'dar, the caster must make a fort save vs DC 15 + rounds of Con'dar or suffer damage equal 4x the duration of the Con'dar. On a successful save this damage is subdual instead. Regardless of save, the caster is exhausted until they receive at least 8 hours of rest and their confessor's touch ability doesn't begin recovery until they're no longer exhausted.