To solve this problem we will consider the definition of Minimum Energy, as the change between the minimum voltage and its distance. Mathematically it can be written as
[tex]E_{min} = \frac{V_{min}}{r}[/tex]
Rearranging to find the Voltage,
[tex]V_{min} = E_{min} \times r[/tex]
Replacing,
[tex]V_{min} = (3.0) \times (0.95*10^4)[/tex]
[tex]V_{min} = 28500V[/tex]
Therefore the minimum voltage needed between your finger and the doorknob to generate this spark is 28.5kV