Superannuation has two components at death, tax free (the after tax money you added) and taxable (the before tax money added by you and your employer and any money from earnings of all the money inside super), so you will have a taxable component.
The tax free component gradually gets diluted by earnings. This is why financial advisors suggest taking out payments each year after you are getting tax free super pension payments, and recontributing them. This dilutes the taxable component, because what you’re putting into super is all tax free.
The taxable component is taxed at death if super doesn’t go to a dependent etc.. The tax is at their taxation rate, generally 15% or 30%, plus 2% Medicare levy. The tax free component isn’t taxed. However, you can’t separate the two - if 20% of your super is taxable, then 20% of what anyone receives is taxable.