Your wife is responsible for paying the zakat on her gold. If she can’t get hold of it and she is unable to sell it because they are keeping it and not releasing it, there is no zakat on her until she receives it.

Sheikh, my wife says her mom gave her certain amount of gold which is above nisab level, problem is its not under my possession or under my wife possession, i never know how much they gave her, its not with her right now, its been more than 7months, and i dont think i can exercise full rights on the gold without anyones permission, so in that case am i responsible to pay zakat ?