What would be the wingspan for a 35 kg bird?

The heaviest living flying bird is the kori bustard of Africa. Large males weigh up to 20 kg, but no heavier specimens have been reliably reported. So there is no flying bird that weighs 35 kg, and the wingspan of flightless birds is really a rather different proposition. So your question really has no good answer.

But let's try for a not-very-good answer. A big kori bustard has a wingspan of up to 275 cm. If you were to scale up a 20 kg, 275 cm individual to 35 kg, you'd be increasing its mass by a factor of 35/20 = 1.75, which means you'd be increasing its linear dimension by the cube root of that factor, about 1.205 (since 1.205^3 = 1.75). That would give it a wingspan of 332 cm.

But it gets better: the teratorn Argentavis, which lived about 25 million years ago in Argentina, is the largest know flying bird, and it was a lot bigger that a kori bustard. Mass estimates are in the region of 80 kg, and wingspan estimates between 6 and 8 meters. See http://en.wikipedia.org/wiki/Argentavis