When Dokja calls someone a liar to their face, he can tell if whatever statement came before was a truth or a lie. If he correctly guesses that someone was lying to him, he can control them once, in a degree relatively proportional to the lie that was told. So like. If someone tells a little white lie he cannot do a lot. But if say someone claimed they loved him when they did not the compulsion can be quite powerful.

Obvs this is all limited by 'what is fun for the other person' it is not beyond being resisted.

If Dokja FAILS and the person was telling the TRUTH, the power rebounds on him and they can proportionally control him. But it's not like he explains this to them so fairly frequently people never realize it happened. They have to stumble onto that part of it.

Dokja does NOT announce he has this power, he tries quite hard to keep it a secret.