Answer
$m\widehat{CD}=52^{\circ}$
Work Step by Step
We must know that the measure of a minor arc is equal to the measure of its corresponding central angle.
In the given question, we can see that the corresponding angle of minor $\widehat{CD}$ is $\angle CPD$.
This implies that $m\widehat{CD}=m\angle CPD$
Now, $m\angle CPD=180^{\circ}-m\angle TPC=180^{\circ}-128^{\circ}=52^{\circ}$
Thus, $m\widehat{CD}=52^{\circ}$
