Answer
$m\widehat{DB}=90^{\circ}$
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 $\widehat{DB}$ is $\angle DPB$ .
We have: $m \angle DPB=90^{\circ}$, so
or, $m\widehat{DB}=90^{\circ}$