(1) The land which your wife owns, if she has bought it with the intention of selling, then zakah shall be wajib on the value of that land (as per the current rate) though the land is not used in any way. And if she did not buy it with the intention of selling rather it was taken with other intention or the land is ancestral then there is no zakah on that land.
(2) Here too the ruling is the same i.e. if it was bought with the intention of selling then zakah shall be paid in the last of the year on the total value of the land including the rent; otherwise zakah shall be wajib only on rent provided it reaches up to the nisab.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband