Answer
$\exists x\in D(P(x)\wedge \forall y\in D(P(y) \leftrightarrow y=x))$
Work Step by Step
We can write:
$\exists x\in D(P(x)\wedge \forall y\in D(P(y) \leftrightarrow y=x))$
The statement is a conjunction of two statements. The first statement simply says that there is an element $x$ in $D$ for which the predicate $P$ is true. The second statement involves a biconditional. It says that if there is any other element $y$ in $D$ for which $P$ also holds, then it must be identical to $x$ and vice versa.
