From "Rescue Party" by Arthur C. Clarke...
"He increased the magnification until only the center portion of the nova was visible. Close to its heart were two minute condensations, one on either side of the nucleus.
'Those are the two giant planets of the system. They have still managed to retain their existence—after a fashion. And they were several hundred million miles from the sun. The nova is still expanding—but it's already twice the size of the Solar System.'"
Yes, this is science fiction from 1946, but it actually seems to be pretty accurate.
A more scientific analysis
It has often been claimed that a supernova can radiate as much energy as the Sun will in its entire lifetime.
10 billion years * 365 days * 86400 seconds * 3.8 * 10^26 J/s = roughly 10^43 Joules of energy.
Now, to find the binding energy of the gas giant(to see if it even survives the explosion)
E = 3GM^2/5R. Let's use Jupiter as an example.
(3 * (6.67 * 10^-11) * (10^54 kg))/(5 *(6.6854 * 10^7 m)) = 10^35 J.
The gravitational binding energy of Jupiter is eight orders of magnitude less than the total amount released by the supernova.
"But Jupiter's orbit is 2.444 billion kilometers in circumference!" says the annoying man in the back row. "Surely all of that energy cannot be distributed in a cone directly at it!"
sqrt(6.6854 x 10^5 km Jupiter radius/7.606 * 10^18 kilometers orbital "surface area") = ~8.7 * 10^-13. Multiply by 10^43. Yep, Jupiter is toast. Within an order of magnitude of the necessary gravitational binding energy, but most of the upper atmosphere will boil off. The most you can probably hope for is a rapidly expanding plasma cloud. At that point, it doesn't really matter whether it still orbits the white dwarf or not, you at most will only have an Earth-mass barren rock anyway.
TL;DR: Your gas giant is toast unless it is very far from the host star. Hope you weren't using it for a fusion candle.