Is zakat obligatory on a property prepared for rent, or only on the money derived from it, and what is the nisab for money zakat?

The aforementioned transaction is neither a lease, nor a sale, nor a partnership. The contract must be corrected. It can be corrected by selling the goods and leasing the shop with its fixtures, or by employing your friend to work in the shop for a known wage, with the shop's income belonging to you.

As for zakat: If the goods remain in your possession and are not sold, they are subject to zakat on trade goods by valuing them at the completion of the year. If their value reaches the nisab, either alone or with other money, then 2.5% of their value is to be given. If the goods are sold and only the shop's rent remains, then the cash you possess (from the price of the goods, or the shop's rent, or other sources) is subject to zakat if a year has passed over it and it has reached the nisab; then a quarter of a tenth (2.5%) of it is to be given.