Is zakat due on the amount paid to settle the loan for building the shop?

You are not permitted to take a portion of the profit without the permission of your partner, because it is a debt upon you that must be returned to the Mudarabah capital, as it serves to protect the principal. Zakat becomes obligatory on your share of the profit after its distribution, if it reaches the nisab and a full year has passed while it is in your possession, because ownership is not established until distribution.

The year (for Zakat) for the Mudarib (the working partner) does not begin until the time of profit distribution, because prior to distribution, it is a protection for the principal capital.