Where is Tzar guy at

He was in Royal quarter, the guard with. But now he is totally gone... how can i finish all “persuading thingy” quests

I found him... i had to go all backward from the first island, but I cannot understand why i cannot visit his house directly though

Perhaps you dropped or stashed the Lukomoryan Badge he gave you? You could walk right in if you have that.

Phredd sells it for 50,000 gold if you lost it but it's not sellable in regular shops so you couldn't have sold it.

Oh i put it on my house... thanks