You have the correct axis of symmetry value. Nice work.
Plug that x value into the equation to get...
y = -2x^2 - 12x - 10
y = -2*(-3)^2 - 12*(-3) - 10 <<-- replace every x with -3; then use PEMDAS
y = -2*(9) - 12*(-3) - 10
y = -18 + 36 - 10
y = 18 - 10
y = 8
The vertex is the ordered pair (-3, 8)
Note: the axis of symmetry is the vertical line through the vertex