How do I determine blocking capacitor and bias resistor values for an Electret Microphone?
Well, with a bias resistor (aka load resistor) of 2k2 (as specified in the data sheet picture in the question), the sensitivity figure (-42 dBV/Pa) means that at a sound pressure level of 94 dB (1 pascal), the output voltage of the microphone is -42 dBV or 7.94 mV RMS when the sound is 1 kHz.

With a 10 uF coupling capacitor and a 20 kohm load, the low frequency cut-off is \$\dfrac{1}{2\pi RC}\$ = 0.79 Hz i.e. very sub sonic but perfectly alright for audio.


  I've inherited a design which is not producing a high enough recording
  volume


So, at 1 kHz and 94 dB SPL the mic signal is about 8 mV RMS and the max gain of the amp is 30 dB hence this will produce an output level of 250 mV RMS.

If this level is too low then you need more gain.