Step 1: Use the formula for the potential in a parallel combination of capacitors.
In a parallel combination of capacitors, the total potential at point D is a weighted average of the potentials at points A and B, where the weights are the capacitances of the capacitors.
Step 2: Calculate the potential at point D.
The potential at point D is given by the formula:
\[
V_D = \frac{C_1 V_1 + C_2 V_2}{C_1 + C_2}
\]
Final Answer:
\[
\boxed{\frac{C_1 V_1 + C_2 V_2}{C_1 + C_2}}
\]