3. As shown in Figure 6, given the quadratic function $\boldsymbol{y}=$ $(x+m)^{2}+k-m^{2}$, the graph intersects the $x$-axis at two distinct points $A\left(x_{1}, 0\right)$ and $B\left(x_{2}, 0\right)$, and intersects the $y$-axis at point $C$. Then the other intersection point $D$ of the circumcircle of $\triangle A B C$ with the $y$-axis has coordinates
3. $(0,1)$.

It is easy to find that point $C(0, k)$.
From the given condition, $x_{1}$ and $x_{2}$ are the roots of the equation $(x+m)^{2}+k-m^{2}$
$=0$, which simplifies to $x^{2}+2 m x+k=0$. Therefore,
$$
x_{1}+x_{2}=-2 m, x_{1} x_{2}=k \text {. }
$$

By the intersecting chords theorem, we have
$$
O D=\frac{O A \cdot O B}{O C}=\frac{\left|x_{1} x_{2}\right|}{|k|}=\frac{|k|}{|k|}=1 .
$$

Thus, point $D(0,1)$.